120 BACTERIOLOGY. 
If the bactericidal effect of the serum outside the 
body always went hand-in-hand with the immunity of 
the individual from which it was taken, the immediate 
cause of immunity would be solved and our search be 
directed to find the source and nature of these germi- 
cidal substances; but this is not wholly the case, for 
while in many instances it is so, in others it is as un- 
doubtedly not true. We must, therefore, add to the 
serum the activity of the cells, which produce constantly 
the substances which are partly given up to the blood 
and fluids of the body and partly retained in their own 
bodies. This deleterious action of the blood in bac- 
teria can be increased by infection. Some good ob- 
servers have found that blood in animals naturally 
immune to certain parasitic bacteria, which had little 
or no bactericidal effect, became possessed of it after a 
moderate infection; this seeming to indicate a protective 
effort of the body cells to withstand bacterial invasion. 
Concerning the nature of these non-specific protective 
substances, named alewines by Buchner, we have as yet 
little positive knowledge, but certain properties of them 
are known. ‘They are largely precipitated by a 40 per 
cent. solution of sodium sulphate, but not by alcohol. 
These substances would seem to belong to the so-called 
living proteids, and resemble certain of the globulins 
in their properties, but they are evidently extremely 
complex in their nature. Many of them become inert 
on standing for several months, even at low tempera- 
tures, and after a few weeks at blood-heat. A tem- 
perature above 62° to 70° C. soon totally destroys 
them. Freezing does not affect them. A bactericidal 
serum affects in a deleterious manner the red blood- 
cells of a different species of animals. 
