870 CLOSTRIDIUM 



toxin. Occasionally life may be prolonged for 3 or 4 weeks, and recovery may eventually 

 take place. At necropsy no local lesion is visible at the site of injection ; the mucosa 

 of the small and large intestine is hypersemic. The kidneys are congested, and the liver 

 may show areas of degeneration. Clear urine distends the bladder. In the lungs, which 

 are very congested, there may be infarcts or areas of hepatization. Sometimes oedema 

 or haemorrhages of the central nervous system may be observed, especially round the 

 fourth ventricle. Cultures of the organs are usually sterile. 



Dogs are very much less susceptible than cats, but they may succumb to the disease 

 after subcutaneous injection of toxin, or occasionally after feeding with large doses. Mice 

 and guinea-pigs are highly susceptible, and succumb in 1-4 days. 



Pathogenicity of CI. tetani for Laboratory Animals. 



Tetanus can be reproduced by the inoculation of pure cultures, or of the toxin 

 into mice, rats, guinea-pigs, rabbits, goats, horses and monkeys. Cats and dogs 

 are more resistant ; birds and cold-blooded animals are highly resistant. The 

 most susceptible animal, calculated on the amount of toxin per gram of body 

 weight necessary to prove fatal on injection, is the horse. This is about 12 times 

 as susceptible as the mouse ; the guinea-pig is 6 times, and the monkey 4 times, 

 as susceptible as the mouse (von Lingelsheim 1912, Sherrington 1917). On the 

 other hand, the rabbit is twice, the dog 50 times, the cat 600, and the hen 30,000 

 times as resistant as the mouse (Kitasato 1891, von Lingelsheim 1912). 



Mice. — After the subcutaneous injection of a small quantity of toxin or of pure culture 

 into the mouse near the root of the tail, symptoms develop in about 12 to 24 hours. The 

 spasms start near the site of injection, and spread to the rest of the body, till the animal 

 dies in a state of general tonic contraction. The first symptom noticed is a stiffening 

 of the tail, which becomes erect and is turned towards the side of inoculation ; the hinder 

 extremity of that side becomes stiff, followed later by rigidity of the opposite leg. The 

 contractions pass to the muscles of the trunk, and the mouse develops kyphosis or pleuro- 

 thotonos. Next, the fore-legs become involved, and finally trismus and opisthotonos set 

 in. The contractions occur spasmodically and are succeeded by intervals of rest, during 

 which the animal lies exhausted ; in this phase they can be readily excited by the slightest 

 touch or a breath of air. Death follows in about 24 hours. Post mortem there is little 

 to be seen. There may be sUght congestion and oedema round the site of inoculation, and 

 the spleen may be somewhat enlarged. An exudate of fluid, sometimes blood-stained, 

 may be seen in the pleura or peritoneum. After injection of a pure culture, the bacilli 

 can generally be cultivated from the local site, but are difficult to find under the microscope. 

 The heart's blood and viscera are sterile. 



GurNEA-PiGS. — The experimental disease in guinea-pigs follows much the same course 

 in about the same time as in mice. 



Rabbits. — After subcutaneous or intramuscular injection the incubation period in 

 rabbits is at least 24, and generally 36 hours ; death does not occur for 3 or 4 days. The 

 general tetanic spasms are more marked than in mice or guinea-pigs (Rosenbach 1886). 



Pathogenicity of CI. welchii for Laboratory Animals. 



Intramuscular injection of about 0-2 ml. of an 18-hours' glucose broth culture into the 

 thigh of a guinea-pig usually results in gas gangrene with death in 12-48 hours. Post 

 mortem, there is a large, brawny, crepitant swelling at the site of inoculation, covered 

 with a dark-red, tense layer of skin. The muscle is pale and is undergoing liquefactive 

 necrosis. In the subcutaneous tissue around the local lesion and spreading up to the 

 abdomen, reaching sometimes to the sternum and over to the opposite thigh, is a collection 

 of slightly blood-stained fluid and gas smelling of hydrogen sulphide. The suprarenal 

 glands are often congested, so that the normally sharp differentiation of cortex from medulla 



