Protective Power of Serum of Animals Fed Pneumococci or Tissue of Animals Killed by Pneumococcus.

Abstract

In an earlier paper on the immunization of rats to pneumococcus, produced by feeding the tissues of animals killed by the same organism, brief mention was made of the fact that the blood of the immune animals contains protective antibodies. 1 The present article is a report of the experiments made with sera of rats and dogs. The rats were fed either the infected tissue, the living pneumococcus, or the acid-killed germ. Such animals have already been shown to possess immunity to intraperitoneal injection of virulent pneumococci. 2 , 3 The dogs were fed either the living pneumococcus, or infected rabbit tissue. The object was to learn whether the serum of such animals would protect mice against an intraperitoneal injection of virulent pneumococci. All experiments were done with type I. The preparation of the infected tissue, of the pneumococci, and their feeding, have been described elsewhere. 1 , 2 , 3

To test an immunized rat's serum, the neck was shaved, the rat made unconscious by a blow across the head, the jugular vein cut, and the blood collected and centrifuged. A group of mice would be injected intraperitoneally, with graded doses of a 24-hour culture of pneumococcus, (in a volume of 0.20 cc.) plus 0.20 cc. undiluted serum. Another group of mice would be injected similarly with pneumococcus culture and control rat serum. An additional small group was used to determine the minimum fatal dose of the culture employed. In the dog experiments, some animals were fed the tissues of rabbits killed by pneumococcus, others were fed the living pneumococci. Following the feeding of 275 gm. of tissue, or of the germs from 750 cc. culture per day per dog, for about 2 weeks, the serum was tested in the same manner as the rat serum.