118 MICRO-ORGANISMS AND DISEASE. [CHAP. 



South America does not kill cattle, while it gives them a 

 transitory illness, and after this immunity for a time. 1 Again, 

 Pasteur's " vaccine," which as a rule (but not without excep- 

 tion) does not kill sheep or cattle, is fatal to rodents. 2 From 

 all this it follows that as regards virulence the bacilli an- 

 thracis differ in the different species of animals, and in them 

 acquire different qualities. A culture that does not kill mice, 

 such as an artificial culture of blood-bacillus after one or two 

 weeks' incubation at 20 35 C., or a culture that for other 

 reasons, as when attenuated by heat or antiseptics, does not 

 produce fatal anthrax in guinea-pigs, fails to give to these 

 animals any immunity whatever. Rodents, so far as my ex- 

 perience goes, either die of inoculation with anthrax-bacilli or 

 they do not die ; but they cannot be provided with immunity 

 by any attenuated virus. 



Koch 3 maintains that in neutral chicken-broth the bacilli 

 growing at 42 C. lose their virulence in thirty days, and at 

 43 C. in six days, first for rabbits, then for guinea-pigs, and 

 lastly for mice. I am quite sure from my own observations, 

 that these results are not uniformly obtained, since I have seen 

 anthrax-bacilli very virulent both for rabbits and guinea-pigs 

 even after growing for thirty-six days at 42 G< 5 C. 



Bacillus anthracis is capable, as we have seen, of growing 

 well outside the body, and, when well supplied with oxygen 

 from the air, of forming spores which represent the permanent 

 seeds. Thus if animals, such as sheep and cattle, die of an- 

 thrax in a field, the bacilli of the effusions from such animals 

 (e.g. urine, blood, effluvia from the mouth and nostrils) always 

 contain numbers of the bacilli, and these will be able to grow 

 indefinitely on the surface of the soil, there being always 

 present a large amount of suitable nourishing material, like 

 vegetable and animal decaying matter, and as free access of 

 air is always insured they will eventually form spores. Such 

 soils, owing to the presence of these spores, will remain a 

 permanent source of infection to sheep and cattle sojourning 

 on them (Koch). 



(m} Bacillus tuberculosis (Koch). In all cases of tubercu- 

 losis in man, cattle (Perlsucht) and monkeys, of tuberculosis 



' Roy, Nature, December, 1883. 



2 Klein, Reports of the Medical Officer of the Local Government Board, 18S2. 

 Similar results have been obtained by Gaflky (Mittheil. a. d. k. Gesundheitsamte, 



3 Ueber d. Milzbrandimpfung, 1882. 



Spores of bacillus anthracis stand heating to 100 C. in the dry state for over 

 an hour without being killed ; in the moist state, e. g. exposed to steam at 100 

 C., they are killed after 15 minutes' exposure (Koch). 



