INJVBY TO BACTERIA BY CHEMICAL SUBSTANCES. 39 



gelatin, to which a similar trace of the disinfectant has 

 been added, with fresh material. 



The disinfectant to be tested should always be dissolved 

 in water. (Compare Water, p. 40.) If, because of slight 

 solubility in water, the employment of alcohol in the prep- 

 aration of the stock solution is unavoidable, then special 

 control investigations are required to determine whether 

 the alcohol is injurious in its effects. 



It is found, as well for asepsis as for antisepsis, that the 

 value of the disinfectant is usually much lower if one is 

 working with nutrient media rich in albumin than when 

 working with those poor in albumin. ^ Creolin (Pearson) 

 produces asepsis in bouillon in the proportion of 1 : 15,000 to 

 1:5000, but in beef serum in 1: 150 (Behring). Cholera 

 vibriones, in bouillon free from or containing 1 % of pep- 

 tone, were killed by 0.01% HCl in half an hour, with the 

 addition oi 2f(, peptone by not less than 0.04% HCl in 

 the same time. For descriptive purposes, the test will 

 usually be made in 1 % peptone solution, if one does not 

 wish to employ one of the nutrient media free from albu- 

 min, described on page 34. In any case one will treat the 

 bacteria used for comparison exactly the same, and must 

 give in a paper the finer details employed in the investi- 

 gation. Little is known of varying resistance in bacteria 

 which are free of spores, because of race or nutrient media 

 (compare spores), but there are isolated statements in this 

 direction regarding staphylococci which, perhaps, may 

 point to as yet imperfectly understood resting forms 

 (Esmarch, Z. H. v, 67). 



A combination of disinfectants may enhance the action; 

 the addition of acid (hydrochloric or tartaric acid) espe- 

 cially intensifies the action of sublimate, also of jDhenol and 

 cresol solutions. Moreover, the effect is more certain if 

 the germs are few than if they are abundant, and greater 

 at higher than at lower temperatures. 



' Phenol is an exception. 



