342 BACTERIOLOGY. 



able time, when all the fermentable sugars have been 

 decomposed, more alkaline again through the progress- 

 ing fermentation of other substances. Among the 

 products formed by its growth is the diphtheria toxin. 



Growth in Ascitic Bouillon. Many diphtheria bacilli 

 grow but feebly in nutrient bouillon when first re- 

 moved from the throat. These develop more luxuri- 

 antly when to the bouillon 25 per cent, aseitic fluid or 

 blood-serum is added. 



Growth on Gelatin. The growth on this medium 

 is much slower, more scanty, and less characteristic than 

 that on the other media mentioned, on account of the 

 lower temperature at which it is used. 



Growth in Milk. The diphtheria bacillus grows 

 readily in milk, beginning to develop at a compara- 

 tively low temperature (20 C.). Thus milk having 

 become inoculated with the bacillus from some cases of 

 diphtheria may under certain conditions be the means 

 of conveying infection to previously healthy persons. 

 Though this growth takes place, the milk remains un- 

 changed in appearance. 



Pathogenesis. The diphtheria bacillus is pathogenic 

 for guinea-pigs, rabbits, chickens, pigeons, small birds, 

 and cats; also in a lesser degree for dogs, goats, cattle, 

 and horses, but hardly at all for rats and mice. In 

 spite of its pathogenic qualities for these animals true 

 diphtheria occurs in them with extreme rarity. As a 

 rule, supposed diphtheritic inflammations in them are 

 due to other bacteria which cannot produce the disease 

 in man. 



The virulence of diphtheria bacilli from different 

 sources, as measured by their toxin production, varies 

 enormously. Thus 0.002 c.c. of a forty-hour bouillon 



