106 MICRO-ORGANISMS AND DISEASE. [CHAP. 



(5 to 10 per cent), strong solutions of phenyl-propionic acid 

 and phenyl-acetic acid, corrosive sublimate (i : 10,000), 

 although the spores were kept in these fluids for twenty-four 

 hours and more, did not kill them. 



The spores of bacillu-santhracis are killed by one to two 

 minutes' boiling in water or salt-solution. 



This great resistance of spores to low and high tempera- 

 tures, to acids and other substances, is due to this, that the 

 substance of each spore is enveloped in a double sheath : an 

 internal sheath probably of a fatty nature, and an external 

 one probably of cellulose ; both are very bad conductors 

 of heat. 



Owing to the fact that spores resist the action of boiling 

 water, if not prolonged for ten minutes, and that the other 

 bacteria (such as micrococcus, bacterium, and bacillus itself) 

 are killed by the temperature of boiling water if kept at this 

 temperature for a few seconds, it is possible to separate the 

 spores of bacilli from the other organisms. All one has to do 

 is to subject the fluid containing these various organisms to 

 the temperature of boiling water for a few seconds. All 

 except the spores of bacilli will be thereby killed, and 

 thus the fluid becomes free of all other organisms except 

 the spores. 



When spores are sown in a nourishing material, fluid or 

 solid, and when this is exposed to a temperature of about 32 

 to 38 C., the spores after the lapse of a few hours, in some 

 cases six (spores of anthrax-bacillus), in others two to four 

 hours (spores of hay-bacillus), in others more than six hours, 

 are seen to germinate, each spore growing into a bacillus. In 

 the case of solid nourishing material the presence of moisture 

 is essential. 



In this germination what one sees is this : the spore 

 increases in thickness, it then loses its dark contour at one 



