DEFENSIVE FERMENTS OF THE ANIMAL ORGANISM 43 



having on the one hand the cells of the gut and the 

 liver ready to prevent anything, that is not completely 

 deprived of its own characteristics, from passing 

 into the circulation, and, on the other hand, by having 

 the cells of the body passing on to the blood only 

 such substances as have been so far disintegrated 

 as to have lost those features which harmonize them 

 with the cells. Blood which is in circulation thus 

 always shows the same metabolic products and the 

 same substances ; and from this point of view we may 

 consider the contents of the blood as being always 

 constant. Xo doubt the duty of the lymph, which is 

 placed between the cells of the body and the blood, 

 is to guard the blood against an excess of individual 

 products of metabolism. Probably, also, some of 

 the products, which have been insufficiently disinte- 

 grated, are finally decomposed by the lymphatic 

 glands, or by the lymph itself. 



We are bound in this sense to look upon the lymph 

 system, as indeed we have already pointed out, as an 

 important control station. By means of its own 

 cells, and especially by means of the glands, the 

 lymph watches that no material shall reach the blood 

 which is out of harmony with it. 



From the above point of view we gather an insight 

 into the significance of the invasion of organisms 



r> o 



of all kinds into an animal organism. The isolation 



O 



of the whole organism is immediatelv disturbed when 



