94 ACTIVITIES OF BACTERIA. 



erysipelas. The filtrates through porcelain from the most 

 virulent cultures are without effect ; cultures carefully de- 

 vitalized by short heating or brief action of chloroform, 

 when injected produce only the general effects of protein 

 (fever), and still in these diseases poisoning by the meta- 

 bolic products of bacteria is certainly present. 



It is to be noted as an interesting finding that Petri and 

 Maassen (A. G. A. viii, 318) could demonstrate sulphuret- 

 hemoglobin lines in the fresh blood and edematous fluid 

 of pigs sick with swine erysipelas, — an indication that 

 at least sulphuretted hydrogen poisoning is concerned in 

 the death of the animal. Also in malignant edema a similar 

 demonstration is successful. Hoffa has tried to conceive 

 of rabbit septicemia as poisoning by methylguanidin (Lan- 

 genbeck's Archiv, 1889, p. 273). Emmerich and Tsuboi 

 (Munch, med. Wochenschr., 1893, No. 25, 473)— but cer- 

 tainly without receiving any support — attempt to explain 

 cholera as poisoning by nitrite. 



Certainly these explanations possess great interest, but 

 often they do not suffice, for at least there occur, besides 

 the just mentioned poisoning processes, also specific 

 changes in the blood and tissues of animals, which are 

 proved, among other things, by the generation of specific 

 protective substances (** antibodies "). 



II. Variation in the Virulence of Bacteria. 



The virulence of bacteria is just as variable as are all 

 the other functions (chromogenesis, fermentation, etc.). 

 It is best preserved by continual inoculation of the bacte- 

 ria from one susceptible animal to another. It may also 

 be accomplished in many varieties by rather frequent 

 transfer (about monthly) from one artificial nutrient me- 

 dium to another, but it is best to pass the bacteria through 

 an animal from time to time. On the contrary, the viru- 

 lence usually suffers if, with infrequent transfer, the cul- 

 ture remains long in contact with its accumulated meta- 

 bolic products. 



Reduction of virulence is not difficult to bring about: 



(a) By growing at a somewhat too high temperature anthrax be- 

 comes completely avirulent — at 42.5° in three to four weeks, at 47° after 



