162 ANTISEPTICS AND DISINFECTANTS. 



practical disinfection, therefore, it is important to know what disease 

 germs form spores and what do not. The following are known to 

 form spores : The bacillus of anthrax, the bacillus of tetanus, the 

 bacillus of malignant oedema, the bacillus of symptomatic anthrax, 

 the bacillus of foul brood (infectious disease of bees). The following, 

 so far as is known, do not form spores : The pus cocci (Staphylo- 

 coccus pyogenes albus, aureus, and citreus, and Streptococcus pyo- 

 genes), the micrococcus of pneumonia, the bacillus of typhoid fever, 

 the bacillus of glanders, the bacillus of diphtheria, the spirillum of 

 cholera, the spirillum of relapsing fever. 



Many agents which kill the growing bacteria are incapable of 

 destroying the vitality of spores, and others only do so in much 

 stronger solutions or after a long exposure to their action. 



(c) The number of bacteria to be destroyed. This is an essen- 

 tial factor which has often been overlooked by those making experi- 

 ments. To destroy the bacteria carried over to five cubic centimetres 

 of distilled water by means of a platinum loop, is a very different 

 matter from destroying the immensely greater number in five cubic 

 centimetres of a recent bouillon culture. 



(d) The nature and quantity of associated material. The 

 oxidizing disinfectants, like permanganate of potash and chloride of 

 lime, not only act upon the bacteria, destroying them by oxidation, 

 but upon all organic matter with which they come in contact, and at 

 the same time the disinfecting agent is destroyed in the chemical 

 reaction, which is a quantitative one. The presence, therefore, of 

 organic material in association with the bacteria is an important 

 factor, and if this is in excess the disinfectant may be neutralized 

 before the living bacteria are destroyed. Other substances which 

 precipitate the disinfecting agent in an insoluble form, or decompose 

 it, must of course have the same effect. Thus the presence of sodium 

 chloride in a culture medium would be an important circumstance if 

 nitrate of silver was the agent being tested, as the insoluble chloride 

 would be precipitated. And in the case of mercuric chloride and 

 certain other metallic salts the presence of albumin very materially 

 influences the result. Van Ermengem states that the cholera spiril- 

 lum in bouillon is destroyed in half an hour by mercuric chloride in 

 the proportion of 1: GO, 000, while in blood serum 1: 800 was required 

 to destroy it in the same time. 



(e) The time of exposure is also an important factor. Some 

 agents act very promptly, while others require a considerable time to 

 effect the destruction of bacteria exposed to their action. Thus a 

 solution of chloride of lime containing 0.12 per cent destroys the 

 typhoid bacillus and the cholera spirillum in five minutes, and 

 the anthrax bacillus in one minute (Nissen). On the other hand, 



