SUSCEPTIBILITY AND IMMUNITY. 237 



that while they are present in the cell-free serum they are the prod- 

 uct of certain leucocytes Ehrlich's eosinophile cells. He believes 

 that the eosinophile granules become dissolved in the serum and con- 

 stitute the germicidal proteid which is shown to be present by ex- 

 periments upon bacteria. According to Hankin the separation of 

 these granules can be witnessed under the microscope. They first 

 accumulate upon one side of the cell and then gradually disappear, 

 and as this occurs a considerable increase in the bactericidal power 

 of the serum can be demonstrated. The germicidal power of the 

 blood serum is also said to be increased when the number of leuco- 

 cytes is considerably augmented, as occurs when a sterilized culture 

 of Vibrio Metschnikovi is injected subcutaneously. Also by treat- 

 ment which favors a separation of the alexin from the leucocytes, 

 i.e., a solution of the eosinophile granules. This may be accom- 

 plished by the injection of an extract of the thymus gland of the 

 calf, or by simply allowing the drawn blood to stand for several hours 

 at a temperature of 38 to 40 C. 



Buchner's latest communication upon the subject shows that he 

 also attributes the origin of the germicidal proteid in fresh blood 

 serum to the leucocytes. In his paper on "Immunity," read at the 

 Eighth International Congress on Hygiene and Demography (Buda- 

 pest, 1894), he calls attention in the first place to the fact that a 

 clearly marked distinction must be made between natural immunity 

 and acquired immunity, inasmuch as the " alexins " and " antitoxins " 

 have very different properties. The first-mentioned proteid s are de- 

 stroyed by a comparatively low temperature (55 to 60 C.), while the 

 antitoxins resist a considerably higher temperature, and, unlike the 

 alexins, have no bactericidal or globulicidal action. A very remark- 

 able fact developed in Buchner's experiments is that the blood serum 

 from the dog and from the rabbit, when mixed, neutralize each other 

 so far as their germicidal power is concerned. 



By injecting sterilized emulsions of wheat-flour paste in the 

 pleural cavity of rabbits and dogs Buchner succeeded in obtaining an 

 exudate which had more decided germicidal power than the blood 

 or serum of the same animal. This was evidently due to the large 

 number of leucocytes present, but not to their phagocytic action, as 

 was shown by experiment. By freezing the exudate the leucocytes 

 were killed, but the germicidal action of the fluid was rather in- 

 creased than diminished by freezing. While freezing had no effect 

 upon the germicidal action of the pleural exudate, this was always 

 neutralized by exposure to a temperature of 55 C. 



Emmerich, Tsuboi, Steinmetz, and Low (1892), as a result of ex- 

 tended experiments, arrived at the conclusion that the germicidal 

 action of blood serum " depends upon a specific property of the alkali 



