CHAPTER VII 

 ANTISEPTICS AND DISINFECTANTS 



Many chemical substances have the power of entering into 

 chemical union with the protoplasm of bacterial cells and so 

 forming new compounds, and coagulating the protoplasm; 

 other chemicals dissolve the bacterial bodies. 



Bacteria differ in their powers to resist these agencies; the 

 anthrax spore is much more difficult to kill than the typhoid 

 bacillus; these chemical substances act better at a high than a low 

 temperature. 



A chemical disinfectant, such as copper sulphate, acts more 

 rapidly and effectively in a watery solution than in a complex 

 albuminous one. 



Park's division of the change of viruses under the influence of 

 chemicals is convenient and instructive. Attenuation is the tem- 

 porary restriction of growth, but especially of virulence and 

 pathogenicity; these are resumed upon cessation of action of the 

 chemical. Antisepsis is a definite restriction of growth but there 

 is no destruction. Incomplete sterilization is the destruction of 

 vegetative forms of bacteria but not spores. Disinfection or 

 sterilization is the destruction of all disease producing virus. 



It is often necessary to determine the exact minimum amount of 

 an antiseptic that will destroy a given organism or produce a 

 complete inhibition of growth; for this purpose small amounts of 

 a disinfectant are added to gelatine in test-tubes and these are 

 poured into plates and the result noted. 



Previous to pouring the plates each tube is inoculated with a 

 loopful of culture and thoroughly mixed with the medium. 



