IMMUNITY. 363 



ample, that in septicaemia processes the cell- 

 free aqueous humor of the eye which contains 

 alexins not only fails to kill bacteria, but the 

 bacteria grow in the fluid luxuriantly and mul- 

 tiply, whereas they die off in the blood of the 

 same animals, when it contains cells. It is 

 possible to enclose bacteria in permeable mem- 

 branes and introduce them into the blood or 

 tissue fluids. When this is done, the alexins 

 that are present in solution enter the mem- 

 brane by diffusion, but the wandering cells 

 cannot penetrate it; the result is that the 

 parasites grow in the fluids, although these 

 contain alexin, but perish in the blood of the 

 same animal in which the cells are present. 

 Buchner interprets this latter occurrence by 

 the supposition that in such experiments the 

 number of bacteria introduced is too insignifi- 

 cant as compared with the quantity of the 

 serum, but this explanation can be only par- 

 tially correct. 



Frequently the conditions are extraordinar- 

 ily intricate, so that it is difficult to distin- 

 guish the share of the cells from that of the 

 tissues. When a local disturbance occurs as 

 the result of parasitic invasion, then a reactive 

 inflammation with the formation of a limiting 

 wall of leucocytes takes place, an event that 

 must be considered as a natural healing pro- 



