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 110 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 alexines 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. 



