198 MANUAL OF BACTERIOLOGY. 



acted upon by a known volume strength of disinfectant for 

 a known length of time. Subsequent treatment of the 

 organisms with a suitable inhibitor is necessary when pos- 

 sible, and should growth occur in the cultures following, the 

 test-organism should be recognized in order that possible 

 contamination by extraneous organisms may be excluded. 



In determining the value of germicides for sterilizing 

 ligatures, the students can apply methods based on the fore- 

 going principles. Great care and ingenuity are necessary 

 to arrive at correct conclusions, particularly in the case of 

 animal tendons. In many instances quite stable compounds 

 are formed between tendon and germicide, and living or- 

 ganisms may be so imbedded in such a substance that sub- 

 sequent growth in a test-culture is impossible. The use of 

 a suitable inhibitor, and, prior to final culture-tests, a pro- 

 longed soaking in sterile water, will promote the accuracy 

 of the results. 



CHEMICAL DISINFECTION. 1 



Heat properly applied is the simplest and at the same 

 time the surest disinfectant (see Part I., Chapter II.) ; but 

 for many purposes it cannot be used, and we have recourse 

 to those chemicals that practice and investigation have 

 shown to be of value. The efficiency of chemical disin- 

 fectants as ordinarily used is over-rated. An immense 

 number of substances possess germicidal properties, but un- 

 fortunately, the majority are objectionable in that they are 

 expensive, intensely poisonous, or so corrosive that damage 

 may be done to articles of value with which they may come 

 in contact. 



In the following pages only those substances which are 

 in common use or seem to be of special value will be con- 

 sidered. 



1 For fuller details on this subject consult Rosenau, "Disinfection and 

 Disinfectants," 1902. 



