358 THE DYSENTERY BACILLUS 



Intra- venous inoculation. In the majority of animals death from septi- 

 caemia rapidly follows the inoculation of bacilli into the veins. Post mortem, 

 the intestine is found to be slightly hyperaemic. 



Sub-cutaneous inoculation. The most interesting experimental results are 

 obtained by inoculating animals sub-cutaneously : in rabbits, dogs, cats 

 and young pigs such inoculation is followed by lesions similar to those found 

 in the human subject. Guinea-pigs are less susceptible than other laboratory 

 animals to this method of infection. 



Rabbits. Sub-cutaneous inoculation of 3-4 c.c. of a broth culture is fatal 

 in 4-6 days. 



Inoculation leads first of all to the formation of a large inflammatory oedema 

 at the site of inoculation and this is soon followed by a rise of temperature and the 

 onset of diarrhoea, then paralysis of the hind limbs appears and finally the tem- 

 perature begins to fall and continues to decline steadily until death occurs. Post 

 mortem, lesions are present throughout the alimentary canal being especially marked 

 in the colon. In that portion of the intestine the mucous membrane is thickened, 

 swollen, intensely hypersemic and covered with blood-stained mucus ; small foci 

 of superficial necrosis and haemorrhagic patches are also seen, the former occasionally 

 ending in ulceration. The bacillus multiplies both in the mucus and in the mucous 

 membrane where it is found in pure culture. 



Dogs. A " true representation of human dysentery with its painful and 

 frequent strainings, characteristic stools and lesions " is seen in young dogs 

 as a result of sub-cutaneous inoculation (Vaillard and Dopter). 



Following the inoculation of one or two agar cultures, the temperature rises and 

 an cedematous infiltration appears at the site of inoculation : the animal lies down, 

 seems ill and is apparently in pain, and the motions become frequent and in character 

 similar to those of human dysentery. These symptoms are followed by wasting 

 and a fall of temperature to below normal, and death takes place between the third 

 and sixth day. Post mortem, lesions similar to those described in the case of the 

 rabbit are found in the intestine which is also extensively ulcerated, and the mes- 

 enteric glands are swollen. The bacillus is present in pure culture in the affected 

 parts of the mucous membrane. 



Young pigs. Sub-cutaneous inoculation in these animals generally leads 

 to a fatal attack of dysentery. Post mortem, lesions are found resembling 

 those in the human disease. 



Note. After sub-cutaneous inoculation the bacillus can always be found in the 

 local lesion at the site of inoculation and frequently also in the mesenteric glands, 

 but only exceptionally in the spleen and liver and never in the blood of the heart. 



Bacilli of the Flexner type. 



Bacilli of the Flexner type are far less pathogenic than the Shiga bacillus. 

 Intra-venous inoculation is not followed by severe symptoms and rarely 

 leads to death in the case of dogs and rabbits : intra-peritoneal inoculation 

 is more dangerous and produces a fatal peritonitis in guinea-pigs : feeding 

 experiments give- negative results. Sub-cutaneous inoculation is not followed 

 by the symptoms and lesions of experimental dysentery and does not lead to 

 a fatal result ; after a marked local reaction the animal recovers. 



SECTION II. MORPHOLOGY. 

 1. Microscopical appearance. 



The dysentery bacillus is a small rod-shaped organism morphologically 

 like the colon bacillus ; it measures 1-3/u long. In cultures the organism is 

 pleomorphic, and long almost filamentous forms are found side by side with 

 very short bacilli. It does not form spores, and is non-flagellated and non- 



