ETIOLOGY OF YELLOW FEVER : III. SYMPTOMATOLOGY AND PATHOLOGICAL FINDINGS IN ANIMALS EXPERIMENTALLY INFECTED.

Studies are reported on the type of disease induced in guinea pigs, dogs, and monkeys by inoculating them (1) with the blood or organ emulsions of guinea pigs or other susceptible animals experimentally infected with Leptospira icteroides, and (2) with a pure culture of the organism. Particular attention has been given in these experiments to the clinical features of the experimental infection in the various animals and to the pathological changes resulting from the infection. The symptoms and pathological lesions induced in guinea pigs are much more pronounced than those observed in dogs or marmosets. The period of incubation is nearly the same in all three species, 72 to 96 hours with intraperitoneal or subcutaneous inoculation, and a day or more longer when the infection is induced percutaneously or per os. The febrile reaction in the guinea pig and marmoset is about the same; in the dog there is less fever. The amount of albumin, casts, and bile pigments in the urine is more abundant in the guinea pig and marmoset than in the dog, and these animals also appear on the whole to become more intensely icteric. The black or bilious vomit, however, though occurring frequently in dogs during life, is observed in the guinea pig and marmoset at autopsy. The hemorrhagic diathesis is most pronounced in guinea pigs, less so in marmosets, and least in dogs. In dogs) for example, subcutaneous hemorrhages almost never occur, and the lungs usually show only a few minute ecchymoses. The pleurse, pericardium, and other serous surfaces of the thorax and abdomen remain free from ecchymoses, which, however, with hyperemia, are very marked along the gastrointestinal tract. The symptoms and lesions observed in animals experimentally infected with Leptospira icteroides closely parallel those of human yellow fever. The pathological changes occurring in human cases of yellow fever are similar to those induced by inoculation in guinea pigs and marmosets and in respect to their intensity stand intermediate between those arising in the two animals mentioned.