EFFECT OF CHEMICAL ENVIEONMENT 139 



2. Stability. — The disinfectant, to be most valuable, 

 should be relatively stable in the presence of organic 

 matter. Some of the most powerful of the disinfectants 

 combine with organic matter forming insoluble com- 

 pounds and pass out of solution relatively completely. The 

 strength of the disinfectant may be thereby rapidly de- 

 creased to a point where it no longer destroys micro- 

 organisms. 



3. Hoiiwgeneity. — Disinfectants should he homogeneous 

 in composition. Substances which may be bought in pure 

 condition or in crystalline form such as mercuric chloride, 

 are ideal in this respect. Many of the commercial disin- 

 fectants, particularly those prepared from coal tars, may 

 vary considerably in their composition from time to time, 

 and consequently in their germicidal value. 



4. Solubility. — The ideal disinfectant is one which will 

 dissolve in all proportions in water. 



5. Nontoxic to Higher Life. — ^An ideal disinfectant would 

 be one which is nonpoisonous to man and animals. Obvi- 

 ously disinfectants which will kill one kind of cell and 

 not injure another are difficult to find. Most of the valu- 

 able disinfectants are more or less injurious to tissues. 

 Certain disinfectants, however, may be injected into the 

 blood, exerting a more harmful influence upon microor- 

 ganisms than upon tissues of the body, destroying the 

 former without seriously injuring the latter. Such, for 

 example, is the salvarsan used in the treatment of syphilis. 



6. Noncorrosive. — Inasmuch as disinfectants must fre- 

 quently be used in contact with metal surfaces it is highly 

 desirable that they should not attack metals, injure 

 fabrics, leave stains, or bleach color. 



7. Penetration. — Disinfectants differ decidedly in their 

 power to penetrate materials to be sterilized. An ideal 

 disinfectant is one which penetrates rapidly and effici- 

 ently. 



