KOCH : THE SPORE OF ANTHRAX 243 



to do in vain in forcing the rods of the anthrax to 

 produce spores. Furthermore he gave to this spore an 

 important place, which it has not since lost, in the eti- 

 ology of the disease. He did this by showing that it 

 always forms in the blood and tissues of an animal dead 

 of anthrax, if the temperature is suitable and there is 

 sufficient oxygen. 



These two conditions are necessary. Below 18C, 

 spores are not formed; at 30C. they occur at the end of 

 30 hours; at 35C., in 20 hours. The rapidity with which 

 spores are formed is, therefore, directly proportional to 

 the amount of heat. Oxygen is also indispensable. 

 Anthrax blood, if deprived of this gas, ceased to be vir- 

 ulent in 24 hours without putrefaction. When the 

 blood is allowed to putrefy, the virulence also disap- 

 pears if putrefaction exhausts the oxygen quickly 

 enough so that the spores have not time to form at the 

 temperature to which they are exposed. If the spores 

 have already formed, putrefaction does not kill them 

 or prevent them from developing ultimately on the same 

 field or in the same region if circumstances are favor- 

 able. All the contradictory results of previous investi- 

 gators on the duration of the virulence of the blood 

 or of diseased organs, some saying that it could persist, 

 others that it was lost immediately, were at once 

 explained. The persistence of the disease and its 

 return in an infected country was also explained, 

 and in an entirely natural way. It was the spore which 

 was the agent of preservation, which persisted where 

 the conditions of temperature and of aeration had per- 

 mitted it to form, and where it always held itself in 

 readiness to make new victims. 



Koch was not satisfied in thus broadly explaining 

 the etiology of the disease. He studied the mode of 

 transmission, proved that the symptoms of natural 



