IX SUSCEPTIBLE ANIMALS. 411 



acid in six hours (Hueppe). Pasteur (1880) has shown that when 

 cultures of this bacillus (microbe of fowl cholera) in bouillon are 

 kept for some time they gradually lose their pathogenic virulence, 

 and he has ascribed this "attenuation of virulence" to the action of 

 atmospheric oxygen. He also ascertained that the particular degree 

 of virulence manifested by the mother culture after a certain interval 

 could be maintained in successive cultures made at short intervals. 

 He was thus able to cultivate different pathogenic varieties, and to 

 use these in making protective inoculations, by which susceptible ani- 

 mals were preserved from the effects of virulent cultures injected 

 subsequently. 



Attenuated cultures recover their virulence when inoculated into 

 very susceptible animals. Thus a culture which would produce a 

 non-fatal and protective attack in a chicken may, according to Pas- 

 teur, kill a small bird, like a sparrow; and by successive inoculations 

 from one sparrow to another the original degree of virulence may be 

 restored, so that a minute quantity of a pure culture would be fatal 

 to a chicken. 



Pathogenesis. Pathogenic for chickens, pigeons, pheasants, 

 sparrows, and other small birds, for rabbits and mice, also for swine 

 (Schweineseuche), for cattle (Rinderseuche), and for deer (Wild- 

 seuche). Subcutaneous injection of a minute quantity of a virulent 

 culture usually kills chickens within forty-eight hours. Some time 

 before death the fowl falls into a somnolent condition, and, with 

 drooping wings and ruffled feathers, remains standing in one place 

 until it dies. Infection may also occur from the ingestion of food 

 moistened with a culture of the bacillus or soiled with the discharges 

 from the bowels of other infected fowls. At the autopsy the mucous 

 membrane of the small intestine is found to be inflamed and studded 

 with small hsemorrhagic foci, as are also the serous membranes ; the 

 spleen is notably enlarged. The bacilli are found in great numbers 

 in the blood, in the various organs, and in the contents of the in- 

 testine. In rabbits death commonly occurs in from sixteen to twenty 

 hours, and is often preceded by convulsions. The temperature is 

 elevated at first, but shortly before death it is reduced below the 

 normal. The post-mortem appearances are : swelling of the spleen 

 and lymphatic glands ; ecchymoses or diffuse hsemorrhagic infiltra- 

 tions of the mucous membranes of the digestive and respiratory pas- 

 sages, and in the muscles ; and at the point of inoculation a slight 

 amount of inflammatory oedema. The bacilli are found in consider- 

 able numbers in the blood within the vessels, or in that which has 

 escaped into the tissues by the rupture of small veins. They are not, 

 however, so numerous as in some other forms of septicaemia e.g., 

 anthrax, mouse septicaemia when an examination is made imme- 



