Immunization Against Pneumococcus by Feeding Desiccated or Milk Suspended Organisms.

Abstract

The author previously demonstrated that white rats can be protected against many lethal doses of pneumococci, intraperitoneally injected, if these animals are first fed either the tissues of animals killed by this germ, 1 living pneumococci, 2 or HCL killed germs. 3 It was next decided to determine whether the acid killed germ when dried and mixed with cracker meal and the acid killed germ when still moist and suspended in milk could also be used. The object was to simplify the method of administering the germs as far as possible, consistent with successful immunization. At the same time success or failure accompanying a given modification gradually helps toward an explanation of oral immunization with the pneumococcus.

The organisms were grown, killed and centrifuged as described elsewhere. 3 A thin layer of germs was spread on a watch crystal and warmed on a water bath, so that they were at no time heated above 37° C. Desiccation was complete in 15 minutes. For 20 days each rat was fed the dried germs, 50 cc. of culture per day, mixed with moistened cracker meal. For testing the resistance of control and treated animals, a 24 hour virulent culture was diluted serially and the desired amount injected intraperitoneally in a volume of 0.20 cc. Table I contains the data for this experiment, and gives the rat number, whether control or experimental, its weight, the dose injected and the result. These data show clearly that the rats which were fed the dried pneumococci are considerably more resistant to the virulent germ than the control animals. The experiment was repeated, using larger rats, which responded less regularly than rats of the weights shown in Table I, although to the same degree.