1) 



homologous to the coccus which had caused the infection. In 

 infected rabbits which had developed septicaemia, inhibitory 

 substances appeared in the blood ; and, when immune serum was 

 injected into infected rabbits, the immune substances disappeared 

 very quickly. " When immune serum is administered to patients 

 " severely infected with pneumococci, the immune bodies may also 

 " disappear very rapidly, and this disappearance is probably 

 " associated with the presence of such soluble substances in the 

 " blood." With reference to the observations of Dochez and Avery 

 on specific precipitable substances, he says : — " While it is not 

 " certain that the substances in the infected animals which give 

 " rise to fixation of antibodies are identical with those concerned 

 " in the precipitation phenomenon, it seems likely that this is the 

 " case." The reason why Type II serum was less effective than 

 Type I might be " not only because its concentration of immune 

 " bodies is less than that of Type I serum, but also because the 

 " power of pneumococci of this type to produce fixing substances 

 " is more highly developed than is that of pneumococci of Type 

 " I." Apparently a similar reason might account for the relative 

 inemcacy of Type III serum. 



Protection Tests on Mice. 



The results of protection tests on mice are often found to run 

 parallel with those obtained by agglutination and precipitation, 

 i.e., the potency of the immune sera may appear to be equally 

 well demonstrated by each of the three methods. But this 

 parallelism is not found invariably. The Rockefeller investi- 

 gators have discussed this question in relation to the standardi- 

 sation of immune sera and have advanced reasons for adopting 

 the protection test on mice as the best criterion. They say* : — 

 " In any case, however, the hope of devising a method of 

 " standardisation, employing either agglutination or bacteriotropic 

 " action, has been destroyed by the observation that, while there is 

 " frequently some gross quantitative relationship between the 

 " protective action of a serum and its agglutinating or bacterio- 

 " tropic power, this relationship is inconstant. For instance, we 

 " have had sera with high protective power and little or no 

 " agglutinating power and vice versa." 



Experiments on Monkeys and Rabbite. 



Recent experiments on monkeys indicate that the problem 

 of pneumococcal immunity in relation to serological types is 

 somewhat complicated. 



Cecil and Blakef vaccinated monkeys by subcutaneous 

 injection of living cultures of Type I and found that active 



* Monographs of the Rockefeller Institute for Medical Research. No. 7 

 p. 54. 1917. 



t Journ. Exper. Med. XXXI, p. 657 and p. 685. 1920. 



