TEXT-BOOK OF BACTERIOLOGY. 201 



ment of an anthrax bacterium to its conclusion ; from the bacillus 

 to the spore, and from the spore round again to the bacillus. 



It is true that the process is not always completed as above 

 described. If the conditions of growth and nourishment are less 

 favorable, the rod-cells become atrophied. The anthrax bacillus 

 has a decided inclination to produce involution forms, which gener- 

 ally appear as lumpy, swollen, irregular bodies. 



The healthy development of the bacilli depends on the proper 

 nourishment, of which we shall speak presently, and also on proper 

 temperature and atmospheric conditions. Under 16 C. this bacil- 

 lus cannot live, and the upper limit is about 45 C.; the optimum of 

 temperature is at about 37 C., yet 30 C. suffices to enable it to 

 develop very luxuriantly and perfectly. In our artificial cultures 

 Bacillus anthracis shows itself very sensitive to a want of oxygen. 

 A slight diminution of this gas is sufficient to check its growth, 

 while in the living body other conditions prevail. 



The occurrence of sporulation depends on the fulfilment of 

 special conditions. 



It takes place only within certain limits of temperature, in par- 

 ticular not under 24 to 26 C.; therefore as a rule not in our ordi- 

 nary gelatin, which, as we know, cannot be exposed to such a tem- 

 perature without losing its solid character. Further, there must 

 be an unchecked access to oxygen. This explains the fact that the 

 anthrax bacillus forms no spores in the living bodies of animals or 

 in their uninjured dead bodies, and that in fluids of some depth 

 when the bacteria sink to the bottom sporulation hardly ever takes 

 place. The best fields for the development of spores are, therefore, 

 the surfaces of our solid media, agar and potatoes, and then shal- 

 low vessels of bouillon or highly-diluted human urine, etc., which in 

 all parts are accessible to the air. 



These facts point also to the cause of the fruit formation. The 

 formerly often-mentioned exhaustion of the food medium has cer- 

 tainly very little to do with it, for there is no difficulty in bringing 

 about an extensive and rapid sporulation in a rich food solution, 

 which would nourish a thousand times more bacteria than it con- 

 tains. It seems, on the other hand, as already mentioned, as if the 

 occurrence of sporulation was the expression for the culminating 

 point of growth in the anthrax bacillus as well as in other plants, 

 and as if it showed an extremely perfect stage of development. 



It is remarkable that the anthrax bacilli in some circumstances 

 permanently and completely lose the power of producing spores. 

 Lehmann, Heim, Buchner, and particularly Behring, have described 

 these sporeless varieties, which differ in no other respect from the 



