THE HAT VIRUSES 445 



Danysz found that the grey rat is only moderately susceptible to infection, and 

 that the organism loses its virulence after a few passages through rodents of this 

 species. He has however succeeded in overcoming the immunity in the following 

 manner : the bacillus is first of all grown in sealed ampoules, then in collodion sacs 

 in the peritoneal cavities of a series of rats, then passed through a mouse and finally 

 through a series of rats (first young rats and subsequently older ones). Danysz by 

 this means obtained a strain which is virulent for grey rats (Mus decumanus), black 

 rats and winter rats (Mus rattus) and which has been placed on the market for the 

 purpose of exterminating rats by means of the epizootic which it produces. 



In view of the researches of Bainbridge which have shown not only that the 

 bacillus typhi murium and Danysz' s bacillus are pathogenic to man but also that 

 other so-called rat viruses " harmless to man and domestic animals " are no other 

 than pure cultures or mixtures of the Salmonella group, great care is required in 

 handling these viruses. There can be no doubt but that human epidemics other 

 than those recorded by Shibayama have resulted from insufficient care in dealing 

 with such viruses. 



7. THE BACILLUS OF PSITTACOSIS. 1 



Psittacosis is an infectious disease of parrots and paroquets of which the causal 

 agent is a bacillus first isolated by Nocard. 



The organism is a member of the Salmonella group and is identical with the 

 aertrycke bacillus (Bainbridge). 



The bacillus is found in the bone marrow and in the blood of infected birds (Nocard). 

 Gilbert and Fournier also isolated an organism similar to the bacillus of psittacosis 

 from the intestines of healthy parrots. 



It is said that the disease may be transmitted to man by contact with the feathers 

 of an infected bird or with the cage in which an infected bird is confined. 



Parrots and paroquets are readily infected by experimental methods.. Sub- 

 cutaneous and intra- muscular inoculation often fail, but intra- peritoneal, intra- 

 venous and intra-tracheal inoculation, and ingestion, set up an infection which 

 proves fatal in a few days. Infected birds sit huddled up and motionless on their 

 perches with their feathers ruffled and wings drooping. They suffer from diarrhoea, 

 refuse their food and are in a constant state of drowsiness. 



Mice, fowls and pigeons can also be infected. Rabbits and especially guinea-pigs 

 are more immune. 



The bacillus of psittacosis being identical with the aertrycke bacillus it follows 

 that the same methods of isolation and identification are applicable to the former as 

 to the latter. 



8. BACILLUS ICTEEOIDES. 



This bacillus was isolated from cases of yellow fever and for a time was considered 

 to be the cause of the disease, which is however now known to be due to a filter- 

 passing organism. The bacillus icteroides is a member of the Salmonella group, and 

 has been proved to be identical culturally with Salmon and Smith's hog cholera bacillus 

 (bacillus aertrycke). No absorption tests however appear to have been carried out 

 so that it is uncertain whether it is a paratyphoid B, an aertrycke or a gaertner 

 bacillus. 



1 L. Psittacus and Gr. ^trra^os, parrot. 



