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, 
2.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 proteids 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 Léw (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 
