DISINFECTANTS AND ANTISEPTICS. 197 



may be used; for formaldehyde, ammonium hydrate; for car- 

 bolic acid, sodium sulphate. 



The testing of gaseous disinfectants, such as sulphur dioxid 

 and formaldehyde, should be conducted under conditions as 

 nearly identical with those met with in. actual practice as pos- 

 sible. The test-organisms may be exposed on threads or glass 

 rods, and acted upon by a known volume of strength of germi- 

 cide for a known length of time. Subsequent treatment of the 

 organisms with a suitable inhibitor is necessary when possible, 

 and should growth occur in the cultures following, the test- 

 organism should be identified in order to exclude possible con- 

 tamination by extraneous organisms. 



In determining the value of germicides for sterilizing liga- 

 tures, the students can apply methods based on the foregoing 

 principles. Great care is necessary to arrive at correct conclu- 

 sions, particularly in the case of animal tendons. In many in- 

 stances quite stable compounds are formed between tendon and 

 germicide, and Uving organisms may be so imbedded in such 

 a substance that subsequent growth in a test-culture is impos- 

 sible. The use of a suitable inhibitor, and, prior to final culture- 

 tests, a prolonged soaking in sterile water, will promote the 

 accuracy of the results. 



So many and often such obscure chemical and physical fac- 

 tors enter into the action of chemical germicides that uni- 

 form results are not possible within narrow limits. This ac- 

 counts for the conflicting results obtained by different investi- 

 gators, and even by the same investigator at different times. A 

 number of variable and only partially controllable conditions 

 enter into every test. Results with gaseous disinfectants are 

 especially uncertain on this account. None of them have any 

 great power of penetration, and consequently act only where 

 the bacteria are freely exposed and then not always with 

 certainty. 



