IMMUNITY. 361 



action perhaps goes on in the intestine, where 

 the peptones of digestion, which produce a 

 poisonous effect when injected directly into 

 the circulation, are made harmless by being 

 converted back again into proteid by the epi- 

 thelium cells. 



The organism, therefore, has at its disposal 

 certain purely chemical aids, variously devel- 

 oped in the various organs, tissues or cells, 

 for rendering innocuous the foreign, active or 

 ferment-like soluble poisons, and it also pos- 

 sesses substances in solution in the body- 

 fluids, which are able to weaken parasites and 

 destroy them. 



The protective power of the blood is only 

 manifested plainly outside of the body in the 

 cell-free serum ; as H. Buchner discovered, it 

 is diminished and eventually destroyed, in 

 proportion to the amount of haemoglobin with 

 which the serum is mixed, a fact which ex- 

 plains why it is that the blood-poisoning dis- 

 eases are so likely to run a fatal course. Ac- 

 cording to Hankin, the protective substances 

 of the blood serum are derived from the leuco- 

 cytes of the blood ; they are, so to speak, 

 proteid substances made active through the 

 intervention of the living cells, and like 

 the enzymes they survive the cells form- 

 ing them. Emmerich, accordingly, postu- 



