IMMUNITY AGAINST THE PNEUMOCOCCUS 247 



taken in connection with the fact that in man the organisms are 

 found in the greatest numbers in the lung, suggest that a toxic 

 action is at work. Various attempts have been made to isolate 

 toxins from cultures of the pneumococcus, e.g., by precipitating 

 bouillon cultures with alcohol or ammonium sulphate, and 

 poisonous effects have been produced by certain substances thus 

 derived ; but the effects produced are, as in so many other 

 similar cases, of a non-specific character, and to be classed as 

 interferences with general metabolism. The general conclusion 

 has been that the toxins at work in pneumonia are intracellular ; 

 but no special light has been thrown on the common effects of 

 the members of this group of bacterial poisons. As in other 

 cases, however, we have to reckon with the distribution in the 

 infected body of poisonous substances consequent on lysis of the 

 infective agent. 



Immunisation against the Pneumococcus. Animals can be 

 immunised against the pneumococcus by inoculation with 

 cultures which have- become attenuated by growth on artificial 

 media, or with the naturally attenuated cocci which occur in the 

 sputum after the crisis of the disease. Netter effected immun- 

 isation by injecting an emulsion of the dried spleen of an animal 

 dead of pneumococcus septicaemia. Virulent cultures killed by 

 heating at 62 C., rusty sputum kept at 60 C. for one to two 

 hours and then filtered, and filtered or unfiltered bouillon 

 cultures similarly treated have also been used. In all cases one 

 or two injections, at intervals of several days, are sufficient for 

 immunisation, but the immunity has been observed to be 

 usually of a fleeting character and may not last more than a few 

 weeks. The serum of such immunised animals may protect 

 rabbits against subsequent inoculation with carefully regulated 

 doses of pneumococci, and if injected within twenty-four hours 

 after inoculation, may prevent death. 



The Klemperers treated a certain number of cases of human 

 pneumonia by serum derived from immune animals and appar- 

 ently with a certain amount of success. The serum at present 

 most used is that prepared by Merck according to the principles 

 laid clown by Homer. This observer found that specially 

 vigorous growths of the pneumococcus could be obtained when 

 it was grown on sheep-serum glycerin bouillon. The principle 

 underlying the preparation of his anti-serum, however, is founded 

 on the view of Ehrlich, that, in order to obtain immune bodies 

 likely to be complemented by human serum, all the antigenic 

 qualities of an organism must be brought out, and this can 

 only be done by immunising different species of animals and 



