302 BACTERIA. 



found that the diphtheria bacillus has a tendency to lose 

 its virulence on cultivation. 



It was at first concluded that the bright, strongly refrac- 

 tile particles and deeply stained granules were more or 

 less perfectly developed endospores, and that some of the 

 involution forms might possibly be arthrospores. Although, 

 however, the organisms remain alive and potentially active 

 after being subjected to drying for a considerable time, a 

 moist temperature of $8° C. is quite sufficient to kill them 

 off, which would scarcely be the case were these bodies true 

 spores. 



The bacillus, as we have seen, grows freely on meat fluids that have an 

 alkaline reaction, but as it grows it first renders these media slightly acid, 

 but later, if there is free access of air, the fluid again becomes alkaline. 

 The acid reaction is always most marked in those cases in which there is 

 glycerine in the cultivation medium. The organism grows " in vacuo," 

 but more slowly than in air ; the exclusion of air, however, interferes with 

 the formation of acid, so that under these conditions the bacillus may retain 

 its vitality for a period of six months, or even longer. Examined in a fluid 

 medium it is found to be quite motionless. 



Although Loffler was able to produce some of the symp- 

 toms of diphtheria by the inoculation of this bacillus on an 

 excoriated mucous membrane, he was not satisfied that this 

 was the real causa causans of the disease, and it was left for 

 Roux and Yersin to demonstrate the intimate causal relation 

 that actually exists between this organism and true diphtheria. 

 They repeated LofHer's experiments of inoculating the bacilli 

 on the damaged mucous membrane of rabbits, guinea-pigs, 

 and pigeons, and in all cases they found that characteristic 

 diphtheritic patches were produced. Injected under the skin, 

 the bacillus causes swelling at the point of inoculation, and the 

 animal dies with symptoms of acute poisoning. In some cases 

 there is found congestion and effusion into the serous cavities ; 

 in others there is evidence of fatty degeneration, of the liver, 

 similar to, but more acute than that met with in cases 

 of diphtheria in the human subject. A very important 

 point determined by them was, that if death did not take 

 place too rapidly, characteristic diphtheritic paralysis usually 

 supervened. The bacillus in these cases was found only at 

 the point of inoculation, and even in the most congested 

 organs it could not be demonstrated either in the blood 

 channels or in the lymph spaces, whilst it often disappeared 



