RELATIONS OF THE ORGANS TO ONE ANOTHER. 597 



the entire anatomical construction of the animal tissue and with our 

 ideas of metabolism. 



It would be, in fact, hard to understand why the separate tissues 

 should be so much differentiated if the essential part of metabolic pro- 

 cesses consisted merely in enabling the cells already formed to retain their 

 constituents and in furnishing them merely with sufficient heat units for 

 the exercise of their functions. If even the digestive process, which 

 a priori appears so simple, requires such a fullness of chemical processes, 

 utilizes so many organs, and reacts so sensitively to the different condi- 

 tions which prevail, we may conclude at once that the cell-metabolism 

 certainly cannot proceed along altogether simple lines, but that here 

 also secretions from certain groups of cells must be of considerable sig- 

 nificance. We hold that it is not entirely impossible that every indi- 

 vidual cell of the body takes part in secretory work, and thus has in some 

 way a favorable effect upon the general metabolism. Perhaps this point 

 of view may give us some idea of the reason why organisms constantly 

 require a certain amount of albumin. Unquestionably the proteins 

 occupy a quite different position in metabolism from that taken by the 

 nitrogen-free foodstuffs. We can well imagine that they are required 

 chiefly for the formation of secretions. We do not overlook by any means 

 the fact that the large requirement of albumin is even then only partly 

 explained unless one is ready to assume that in the formation of the secre- 

 tions a large number of cells are disintegrated and therefore must be 

 built up anew. 1 It seems to us very important to state that there is no 

 essential difference between the glands with an excretory duct and thosa 

 in which there is no duct. It is especially doubtful whether we are justi- 

 fied in assuming that only cells arranged in the shape of a gland are 

 active in the formation of secretions. Many facts indicate that the 

 contrary is true. Moreover, there are many intermediate stages between 

 glands with ducts and those with none. The mucous membrane of the 

 intestine secretes intestinal juice, enterokinase externally and secretin 

 internally. The pancreas secretes externally the digestive juice, and also 

 probably secretes substances internally which take part in the metabolism 

 of carbohydrates. Again, the liver undoubtedly has several secretory 

 functions. On the one hand, it yields the bile which, in its formation 

 and the method of giving it up, corresponds to an external secretion. 

 Now we know, for example, that the liver is constantly storing away 

 sugar and assimilating it as glycogen in order that, at the right moment, 

 fermentation may cause the reverse process to take place, i.e. sugar be 

 given up to the blood. Certainly this is an internal secretion just as 

 much as the formation of any other substance under the influence of the 

 cells. To be sure, in this case we know just what this secretion is, 



1 Cf. Lecture XI, p. 221 et seq. 



