US 3072534 A
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United States Patent Patented Jan. 8, 1983 3,072,534 DURABLE ANTIBACTERIAL TEXTILE FINISH FOR CELLULOSIC FIBERS Philip B. Roth, Somerville, and Leonard B. Hallows, New Brunswick, N.J., assignors to American Cyanamid Company, New York, N .Y., a corporation of Maine No Drawing. Filed Feb. 21, 1958, Ser. No. 716,560 7 Claims. (Cl. 167-84) This invention relates to the finishing of textile materials, including fibers and articles formed therefrom, and to methods of imparting a durable antibacterial finish to such textile materials and to the materials thus treated.
More particularly, this invention relates to an antibacterial finish of improved durability for cellulosic textile materials which contains neomycin and an agent for fixing the neomycin more durably to said textile material and to methods of applying the finish and to the textile material so finished.
In recent years, increased attention has been given to the development of textile finishes which have become known as purifying finishes. These finishes are intended to reduce the number of microorganisms residing on the material whereby such materials may be used with less danger from harmful bacteria. These purifying finishes, when applied to articles of clothing worn close to the body, are also helpful in the prevention of the development of odor.
Satisfactory purifying finishes should be durable and activ at low concentrations against a broad spectrum of microorganisms. It should be non-toxic and nonallergenic. It should not have the tendency to sensitize the wearer of the textile material to the material of the finish. It should not have the quality of allowing strains of bacteria to develop which are resistant to the antibacterial agent of the finish. Still further, it should be resistant to home and commercial laundering conditions and should impart little or no modification of the hand of the textile.
Neomycin employed as a purifying finish is highly satisfactory with respect to most of these categories, and its use is described in U.S. application, Serial No. 638,695, filed February 7, 1957, now US. Patent No. 2,830,011, the subject matter of which is incorporated herein by refer ence. The finish imparted by neomycin employed in accordance with thedisclosure of this application to cellulose textile materials provides a very satisfactory and durable finish, which remains anti-bacterial after numerous launderings. This durability is believed to be the result 3 f the neomycin being substantive to the cellulose base aterial.
The retention of this antibacterial finish on cellulosic textile materials containing suitable concentrations of neomycin is excellent in substantially alkali free laundering mediums; however, the antibacterial effect is distinctly reduced when the finished material is laundered under strong alkaline laundering conditions of the type normally employed in commercial laundering operations. Apparently, this results from the alkaline material destroying the substantivity of the neomycin. This shortcoming, while not significant with respect to a large number of the items and materials for which the invention described therein is readily applicable, does subject the general inventive concept to a rather serious limitation.
Therefore, it is an object of the present invention to provide an antibacterial finish containing neomycin for textile materials and in particular cellulosic textile materials, which is durable to the strong alkaline wash conditions, as for example, of the type normally experienced in commercial laundries.
It is a further object to provide cellulosic textile material having a durable finish containing neomycin and methods of providing the same.
It should be noted that the term neomycin" is used herein in its ordinary sense to denote the commercially available product which is called neomycin, it actually being a mixture of two very closely related antibiotics known more specifically as neomycin B and neomycin C. The term is also intended to cover neomycin as just defined, the individual component of the complex or its salts of which the sulfate is the most generally available. Other salts of neomycin have been used in finishing textiles with good results. Among these may be mentioned neomycin parahydrobenzoate, neomycin sulfanilate, neomyc.n-Ntartrate, neomycin propionate, neomycin aconitate, neomycin phthalate, neomycin undecylinate, neomycin palmitate, neomycin stearate and others.
By cellulosic textile material as the term is used herein, it is meant fibers or formed fabric, either woven or felted, containing at least fibers of cellulose origin, and preferably composed entirely of cellulose for maximum effect. As examples of cellulose textile materials, the following are illustrative: cotton, regenerated cellulose, linen, jute, ramie, hemp and the like. Blends of these materials, and combinations of these materials, or blends thereof with wool, silk, nylon, acrylic fibers, polyester fibers, and the like, are also contemplated.
In accordance with the present invention, a method is provided for imparting an antibacterial finish to textile fibers durable to strong alkaline laundering, which comprises the step of contacting said fibers with at least about 0.000l% of neomycin based on the dry weight of the fibers and a water-soluble copper containing fixing agent capable of improving the durability of the said neomycin on the fiber.
As used in the present specification, the term strong alkaline laundering conditions is intended to include laundering in wash water having an alkaline material concentration of 25 parts per 75,000 parts of water and a corresponding pH value of about 10. Norma-11y, these laundering conditions are those employed by commercial laundrres, in which sodium carbonate and caustic soda are the alkaline agents, the concentration of which in wash water may be from between 10 and 50 parts per 75,000 parts of water, and having a pH of from between about 8 and 14. v
The concentration of the neomycin to be applied to the cellulose material may be varied within wide limits depending upon the use to which the particular material is intended. Useful results are obtainable when the fabric contains as little as 0.000l% by weight of the neomycin on the dry weight of the textile material. The preferred range varies from about 0.01% to 1% by weight of neomycin on the fabric. For prophylactic purposes, deposition of from about 0.005 microgram up to 10 micrograms per square centimeter has been found satisfactory with preferred commercial ranges lying between in about 0.1 and about 6 micrograms per square centimeter.
The effective water-soluble copper-containing fixing agents are water-soluble copper sats or dye-fixing agents containing copper. As examples of suitable copper salts, cupric acetate, cupric sulfate, cupric bromide, cupric chloride, cupric nitrate, cupric lactate, cupric fozmate and cupric salicyla-te are examples of those that have been employed successfully.
Examples of water-soluble copper-containing dye-fixing agents which have been found suitable are those agents which increase the fastness of d.re:t dyes on cellulose fibers. These agents are Water-soluble complex resinous copper-containing materials so d under various trade names, e.g., Ahcofix S (Arnold, Hoffman Co), Benzofix CWF (General Aniline and Film Co.), Gyco-fix 67 (Geigy Chemical Corp.), and Cuprofix 47 (Sandoz Chemical Works, lnc.). These materials are water-soluble, resinous condensation products of an aldehyde such as formaldehyde with amides, having copper p.e ent in the form of a simpe salt without direct combination wi.h the resinous component or in complex with said resinous component.
In addition to those designated by their commercial names hereinabove, Naccufix (Allied Chemical and Dye Corp.), another water-soluble copper-containing dye-fixing agent, has been employed with success.
Of the water-soluble copper-containing fixing agents, cupric sulfate and cupric acetate are preferred.
The neomycin may be applied to the textile material by any of the known conventional finishing techniques whereby the material is in contact with the neomycin for a sufficient period of time to fix the neomycin on the material. Thus, for example, it may be applied by padding, spraying, submersion, exhaustion or the like. The watersoluble copper containing fixing agent may be apphed simultaneously with the neomycin from the same bath or from a separate bath either before or after the treatment with neomycin. As a general rule, and because certain of the water-soluble dye-fixing agents are not compatible with the neomycin, these materials are best applied in two stages from separate baths.
After treatment, the cellulose textile material is then dried at room temperature or more rapidly at elevated temperatures as high as 350 F. The materials thus treated have the neomycin present adhered to the base in such a manner as to resist alkaline laundering.
The concentration of the neomycin in the treating solution may be varied within wide limits, depending on the use to which the treated material is intended. When applied by padding, the solution should contain from approximately 0.000l% to 4% and more, by weight of neomycin, as is desired in the dried fabric, since in th padding operation, the fabric is usually impregnated with from about to 150% of the weight of the liquid and then dried. When applied by exhausting, the solution may contain as little as 0.001 microgram per milliliter of solution when highly absorptive cellulosic fibers are treated. From 5 to 500 micrograms of neomycin per milliliter is considered a preferred range for application by exhaustion. For normal prophylactic purposes, sulficient concentrations of neomycin may be substantially adhered to base materials from aqueous treating solutions containing from about 1 microgram to about 400 micrograms per milliliter with preferred commercial limits lying between about 2 and about 200 micrograms per milliliter.
With respect to formed fabrics to which the finish of this invention may be applied, they may take any shape, size or form and are articles which are intended to be re-used. Specific illustrations of such articles would include wearing apparel, handkerchiefs, diapers, hand, dish and bath towels, books and book covers, washable cloth toys, dolls and similar playthings, hospital and hotel sheets and pillowcases, hospital and examination room bathrobes and slippers, barbers and beauticians cloths, and similar articles.
It has been determined that the smallest amounts of copper-containing compounds which give the maximum amount of durability to the neomycin finish on the cellulo ic textile material may be expressed as that amount of copper compound which provides four atoms of copper per mole of neomycin. However, a concentration as low as one atom of copper per 8 moles of neomycin resulted in some improvement of the durability of the neomycin finish. For practical purposes, the limits respecting the relative amounts of the copper compound and the neomycin a e from between 1 atom of copper to 8 moles of neomycin to 8 atoms of copper to one mole of neomycin and preferably from between one atom of copper per 4 moles of neomycin and 4 atoms of copper to 1 mole of neomycin.
The use of more than the amounts of copper per mole of neomycin defined hereinabove is not only uneconomical but also may cause serious discoloration of the fabric, which in the case of white goods could be deleterious. Thus, it is greatly preferred to employ minimum concentrations of the copper compounds, particularly where white goods are being finished.
In accordance with the present invention, it has been determined that only water-soluble copper-containing fixing agents have been effective to improve the durability of the neomycin on cellulosic textile materials to be subjected to strong alkaline washes. Numerous other metallic salts, including those of iron, aluminum, potassium and antimony, chromium, magnesium, manganese, zirconiurn and various mixtures of some of these metallic salts have been employed without success.
In the subsequent examples and tables throughout the present specification, the test referred to therein for the determination of antibacterial activity is a standard one and the treated fabrics are tested by a standard agar plate method. For evaluating the extent of durability of the antibacterial activity of the textile finish, a convenient test method has been devised on inhibition of bacterial growth by a piece of textile placed on an agar plate inoculated with various strains of bacteria. The two commonly used strains are E. coli and S. aureus, which are strains usually employed in the valuation of antibacterial agents for various purposes.
Thus, by determining the antibacterial activity of cloth treated by the process of the invention before and after a number of laundering treatments, the effectiveness of the finish may be determined. The durability of the finish is determined by subjecting the treated textile to a series of repeated launderings. The number of times the material may be laundered before antibacterial activity decreases below an effective level will give a measure of the durability of the finish.
In the test for antibacterial activity, discs of treated fabric of a certain size (11.5 mm. in diameter) are placed on an agar plate and inoculated with the bacterial culture. After two hours contact, the disc is removed and the agar plate is incubated overnight. The degree of inhibition of growth gives an index of the inhibitory effect by the finish on the cloth. This inhibition is easily observed, since the area where the bacterial growth is inhibited remains clear, whereas the remainder of the area Where the bacterial growth has taken place becomes cloudy or opaque. The area under the disc is observed and in addition the total diameter of the area larger than that occupied by the disc results in an area larger than that occupied by the disc itself.
Effective finishes show a clear area at least under the disc with more effective finished areas having a diameter greater than that of the disc itself. If the area of inhibition is greater than the area of the disc, the activity is given as the diameter of the clear area in millimeters. Otherwise, a rating C denotes complete inhibition of bacterial growth under the disc; a rating of P denotes partial inhibition and N rating denotes no inhibition or activity while S and VS denotes slight and very slight inhibition. It should be noted that P is at least 50-75% inhibition, under the test fabric.
As has been noted, the presence of alkaline material, caustic, sodium carbonate, or their equivalents in the Washing or laundering medium as hardening aids, even though slight, as for example, as little as grams of soda ash for 75,000 cubic centimeters volume of the wash liquor, results in a surprisingly marked reduction in the durability of the finish containing neomycin alone. As the amount of alkaline material is increased in the wash liquor, the durability is rapidly decreased to the point where no antibacterial inhibition exists. Antibacterial finishes in accordance with this invention are durable to launderings wherein alkaline materials are employed in the wash liquor.
While it is not known with absolute certainty why the finish of this invention is durable to laundering when the wash liquor contains alkaline materials, and neomycinalone is not, it is believed that the water-soluble coppercontaining fixing agents form complexes with the neo mycin which is not as readily attacked by alkaline materials. This theory, while apparently verified by repeated experimentation, some of which is recorded hereinafter, should not necessarily be binding on applicants by its presentation here.
In order that the present invention may be more fully understood, the following examples are given primarily by way of illustration. No detail or specific enumeration contained therein should be construed as a limitation on "the present invention, except as they appear in the appended claims. All parts and percentages are by weight unless specifically designated.
EXAMPLE 1 62.5 parts of a solution of neomycin sulfate containing 1% of neomycin base were diluted with water at room temperature to give a 0.0625 of solution of neomycin base. 80 x 80 bleached cotton fabric was passed through this solution and the excess removed from the fabric by passing it through a squeeze roll to give an 80% expression. The fabric was dried at about 225 F. The amount on the so treated fabric is .05
EXAMPLES 2-l1 temperature to give a 0.0625% solution ofneomycin' base. 80 x 80 bleached cotton fabric was passed through this solution, and the excess removed from the fabric by passing through squeeze rolls to give an 80% expression. The fabric was dried at about 225 F. The above-treated fabric was then passed through a 0.0625 aqueous solution of the agentslisted above at room temperature. Excess solution was removed by passing through squeeze rolls to give an 80% expression, and the fabric was dried at about 225 F. The treated fabric contained 0.05% of neomycin base and 0.05% of the copper-containing fixing agent on the weight of the fabric.
The results of these applications and that of Example 1 appear in Table I hereinbelow.
EXAMPLES 1118 In these examples, the following agents were employed in the order in which they are listed: ll-Benzofix CWF; 12-Gyc0fix 67; 13 Cu'profix 47; 14-Naccufix; 15-a1uminum acetate; 16-ferrous sulfate; 17-cupric acetate (four atoms of copper per mole of neomycin); and l8-potassium dichromate.
While, in Examples 1-10, the neomycin was applied first and then the fixing agent from separate pad baths, in Examples 1l-18 the procedure was reversed and the fixing agent and then the neomycin were applied to the cotton fabric from separate pad baths.
The general procedure employed in Examples 11-18 was as follows:
x 80 bleached cotton fabric was passed through a 0.0625% solution of the various metallic salt and dye-fixing agent at room temperature. Excess solution was removed by passing the impregnated fabric through squeeze rolls to give an 80% expression and the fabric was dried at about 225 F. The above-treated fabric was then passed through a 0.0625% solution of neomycin base prepared by diluting 62.5. parts of a solution of neomycin sulfate containing 1% of neomycin base at room temperature. The excess solution was removed by passing through squeeze rolls to give an 80% expression. The fabric was then dried at about 225 F. The treated fabric contained 0.05% of neomycin base and 0.05 of metallic salt or fixing agent on the weight of the fabric.
EXAMPLE 19 Operation Temp., Time, Water, g Soap. g Soda F. min ash, g.
1st wash 160 10 2nd wash 160 10 3rd wash 10 10 4th wash. 160 10 1st rinse H0 5 2nd rinse 5 3r rinse. 140 5 4th rinse 140 5 5th rinse 80 5 It was then spun dried and pressed.
The following Table I shows the test results for the combination of neomycin and the various metal salts and copper-containing fixing agents.
In the test values reported in Table I, numerical values denote antibacterial activity greater than the diameter (11.5 millimeters) of the fabric test circle expressed as the diameter of the zone of inhibition in millimeters.
Other values recorded therein are as follows:
Cdenotes activity equal to the area covered by the test circle.
P-denotes at least 50% inhibition under the test circle.
Sdenotes slight inhibition.
VS-denotes very slight inhibition.
N-denotes no activity.
ppartial zone in addition to actual zone measured in millimeters.
Tabl l 1 Uneven inhibition.
EXAMPLE 36 80 x 80 bleached cotton percale was treated for 20 minutes at 80 F. in a solution of neomycin sulfate containing 0.1% neomycin, based on the weight of the fabric. The ratio of solution to fabric was 30: 1. The cotton was turned intermittently during the exhaustion period. After removal from the bath, the fabric was squeezed and dried at about 225 F.
EXAMPLE 37 The above-treated fabric was then passed through a 0.128% solution of cupric acetate monohydrate, and the excess solution was removed by passing the fabric through squeeze rolls to give an 80% expression. The fabric was then dried at about 225 F. The ratio of atoms of copper to moles of neomycin was approximately 4:1.
EXAMPLE 3 8 The above procedure was repeated using a solution of 0.162% of cupric sulfate (CuSO .5H O) in place of the cupric acetate solution. The ratio of atoms of copper to moles of neomycin was approximately 4:1.
The antibacterial activity of the fabrics treated in accordance with Examples 36 to 38 above was measured before and after one alkaline wash. The alkaline wash was that described in Example 22 hereinabove and the results are shown in Table IV hereinbelow.
Table IV Example No 36 37 38 Copper salt None Oupric ace- Cupric sultataH o. fateSHgO. Percent concm. 0.128% 162%.
ZONE or INHIBITION E. coli:
Initial 13.4; 20.2 p 13.3; 18.3 p 12.4; 17.0 p 1 wash--. N 12.0; 13.6 p P-C; 13.8p S. aureus:
Initial 16.5 15.8 15.0. 1 wash N 13.6-- 12.5.
1 Uneven inhibition. 7
As will be seen from Table IV hereinabove, the application of the neomycin to the cotton fabric without the aid of the fixing agents of this invention resulted in the production of an antibacterial finish which was nondurable to an alkaline wash, while the employment of cupric salts in accordance with the present invention and by the employment of exhaustion techniques resulted in an antibacterial finish durable to an alkaline wash.
In addition to the applications carried out in Examples 36 to 38 where the neomycin was applied by exhaustion followed by the application of a copper salt by padding, similar results with respect to the durability of the neomycin finish were obtained when the neomycin and the equivalent copper salts were applied simultaneously from the same bath by exhaustion. It should be noted that where the applications were made without the employment of the cupric acetate or cupric sulfate, the finish was not durable to alkali wash, and those that were, were durable.
EXAMPLES 39 and 40 Two samples of 80 x 80 cotton percale were padded with two solutions containing neomycin sulfate and cupric acetate according to the general procedure set forth for Examples 20-35 hereinabove. These solutions contained the ratio of atoms of copper to moles of neomycin indicated. The antibacterial activity of the treated fabric was measured before and after each of four alkaline washes in order to determine the durability of the antibacterial finish to repeated alkaline washes. The alkaline wash was described hereinabove in Example 19 and the results are shown in Table V hereinbelow.
Table V Example No Example 39 I Example 40 Atoms copper: moles neomycin.
ZONE OF INHIBITION Initial. 14.6; 21.0p 14.
O, 12.6 p P-O; 12.0 p Vs 1 wash 2 washes 3 wa he 4 washes 1 Uneven inhibition.
Table V hereinabove indicates that by application of the principles of the present invention an antibacterial finish comprising neomycin may be rendered durable and effective through four alkaline washes while those applied not EXAMPLE 41 x 8'0 bleached cotton percale was treated with a solution of neomycin sulfate alone and with neomycin sulfate and cupric acetate monohydrate as described in the general procedure for Examples 20-35 hereinabove. The ratio of atoms of copper to moles of neomycin was 4:1.
Samples of the treated fabrics were subjected to a series of alkaline washes wherein the amount of alkali was varied. Three consecutive washes were carried out on each sample in a given concentration of alkali. The antibacterial activity of the samples of fabric was measured before and after the first and third washes of each series of washes.
The washing operation was carried out without bleach or sour in a commercial washing machine (Najort) using four wash cycles and five rinse cycles according to the following schedule:
Soap, g. Alkali 2 es. 1 es.
1 See Table VI.
The load was 6 lbs.
The fabric was then spun dried and pressed.
The test results are shown in the following table.
Table VI hereinbelow records the results of these tests. It illustrates that only through the presence of the copper salt functioning to render the neomycin durable on the cotton percale can the finish withstand alkali washes.
l l l 2 Tablet V! E. 0012' S. aureus p11 Initial 1 wash 3 washes Initial 1 wash 3 washes 8.1,110 alkali Neemycin alone 15.9; 22.7 p C; 12.o p P-C; 12.0 p. 20.0 12.8 12.6.
Nggrycin plus copper aee- 17.0; 21.1p. 12.0; 13.8 p C; 12.0 p 19.6 14.3 13.6. 8.6, 10 g. soda ash ITeordyein alone 15.9; 22.7 p 20.0
Neo nycin plus copper ace- 17.0; 21.1 p, 19.6 9.4, 25 g. soda ash N il ycin alone 15.9; 22.7 p 20.0
Negyein plus copper ace- 17.0; 21.1 p 19.6 9.45, 50 g.soda ash Neam yein alone 15.9; 22.7 p N N 20.0
Neggycin plus copper ace- 17.0; 21.1p VS N 19.6 10.0, 10 g. soda ash, 5 g. caustie. Neauryciu alone 17.7; 22.4 p NZVS 1 N 21. 5
Negtrzreiyein plus copper 2100- 17.8; 22.4 p.- 12.0; 12.8 p 19.9 105,10 g. soda ash, g. caustic--. Neomycin alone 17.7; 22.4 p 21. 5 P-C;1 12,0 13. vs,
Niggrycin plus copper ace- 17.8; 22.4 p 19.9 15.5 12.9. 10.8, 10 g. soda ash, g. caustic.-. Nennyein alone 17.7; 22.4 p N N 21,5 P-C N.
Neg gycin pluscopper aeo- 17.8; 22.4 p. 12.0; 12.6 p.- N 19.9 14.1 S-I.
1 Uneven inhibition.
While the present invention relates primarily to finish- 5. A method of imparting an antibacterial finish to ing of textile materials with purifying finishes containing formed rayon fabric, which finish is durable to alkaline neomycin and copper fixing agents, it will be apparent that laundering, which comprises applying to said fabric from other textile treating agents, lubricants, softeners, Wetting an aqueous solution at least 0.000l% of neomycin based agents and the like may be incorporated in the treating on the dry weight of the fabric and a water-soluble copbaths so long as their presence and function does not per-containing fixing agent for said neomycin, said fixing inhibit or impair the antibacterial finish and its durability agent being selected from the group consisting essentially in accordance with this invention. of water-soluble cupric salts and Water-soluble copper- The neomycin component employable in the present incontaining dye fixing agents. vention, is, for the most part, stable at room temperatures 6. A formed textile fabric, at least 50% of the fibers of over substantial periods of time. However, the combinawhich are selected from the group consisting of cotton tion of the neomycin and water-soluble copper containing and rayon, and characterized by an antibacterial finish fixing agents, if compatible, are usually not stable for durable to alkaline laundering finished by the method acperiods of time in excess of a month at room temperature. cording to claim 1.
Thus, for the most part, it is preferred not to mix the 7. A formed cotton fabric characterized by an antibaccomponents, even when compatible, when storage and terial finish durable to alkaline laundering finished by the shipping times in excess of a month are contemplated. method according to claim 4.
In addition, since ageing of the mixtures sometimes re sults in discoloration, it is generally more desirable not References Cited in the file of this Patent to mix the components until immediately prior to use. 4 UNI D STATES PATENTS We claim: 0
1. A method for imparting an antibacterial finish to g g 1956 formed textile fabric, at least of the fibers of which 2799620 i e a 1957 are selected from the group consisting of cotton and 2830011 i Sman et a July 1957 aiker Apr. 8, 1958 rayon, which finish lS durable to alkaline laundering, 2856 330 Va" O 4 1 5 which comprises applying from an aqueous solution to 50 208606 G ms 1 9 8 said fabric at least 0.0001% of neomycin based on the or on 1959 dry weight of the fabric and a Water-soluble coppcr-con- FOREIGN PATENTS taming fixing agent for said neomycin, said fixing agent being selected from the group consisting essentially of 453,348 France 1913 water-soluble cupric salts and water-soluble copper-con- 9 France J1me 1954 taming dye fixing agents. /88,668 Great Britain Jan. 8, 1958 2. A method according to claim 1 in which at least 0.001% of neomycin is applied to the cotton fabric and OTHER REFERENCES in which the fixing agent is cupric sulfate. Rosenkranl! Oligodynamic Action of pp on 3. A method according to claim 1 in which at least Bacteria, in Archyg-, 89, Pages 253-261 0.00l% of neomycin is applied to the cotton fabric and in Stmcted in Chem- Abstracts which the fixing agent is cupric acetate. Weinberg: The Mutual Effect of Antimicrobial Com- 4. A method of imparting an antibacterial finish to Pounds/and Metallic Cations, P 8 Bacteriologiforrned cotton fabric, which finish is durable to alkaline Cal Reviews, 21, J 11116 1957- laundering, which comprises applying to said fabric from 65 y 6t 511-1 Metal (311615195 of p y XLIV, an aqueous solution at least 0.000l% of neomycin based 1 y 1955, Pages on the dry Weight of the fabric and a water-soluble cop- Weiss et a1.: Bacteriostatic and bactericidal properties per-containing fixing agent for said neomycin, said fixing 0f nfiomycin Proc- Acad- 36, 293 agent being selected from the group consisting essentially of water-soluble cupric salts and water-soluble coppercontaining dye fixing agents.