576 LECTURE XXIV. 



follows from this that in the walls of the blood-capillaries of the mam- 

 mary glands, a liquid rich in lime is secreted, and that, therefore, the 

 endothelial cells of the capillary walls exercise a selection, as is also the 

 case with every cell of all living organisms. 



It is also possible that we are dealing here with a purely physical 

 process in which the gland-cells of the mammary gland constantly uti- 

 lize calcium, i.e., combine with it, and thus cause a continuous dif- 

 fusion of calcium. But here again we shall have to conjecture how 

 this may take place. Even the end-products of metabolism are not 

 carried away, at least not wholly, by a stream of lymph. In this case, 

 likewise, these products can evidently leave the lymph and penetrate 

 into the neighboring blood-capillaries and thus be eliminated more 

 rapidly. The fact that lymph from different places, or even from a 

 single lymphatic fistula at different times, has different compositions 

 speaks in favor of such an assumption. 



Lymph, as we have said, is qualitatively very similar to the plasma. 

 It contains the same substances. Of especial interest is its content of 

 fibrinogen and fibrin-ferment. The amount of each of these substances is, 

 however, very slight. Lymph coagulates slowly, and not all at once. 

 Serum-albumin and serum-globulin are the two principal proteins which 

 have been found in it. Lymph also contains cellular elements, especially 

 the leucocytes, in varying numbers. Unfortunately, we are not very well 

 informed concerning the composition of the tissue-lymph and that of 

 the lymphatics. Most of the analyses that have been made are of lymph 

 obtained from the thoracic duct, which contains chyle. For this reason, 

 we are able to say but little concerning the formation of lymph and its 

 dependence upon definite conditions. On the other hand, the work of 

 Asher 1 and his collaborators has served to explain the relations between 

 the amount of lymph formed and the work of certain organs. The influ- 

 ence exerted by the work of an organ is best illustrated in the case of the 

 salivary glands. If a strip of blotting paper moistened with vinegar is 

 placed in the mouth of a dog, there is a copious secretion of saliva, and at 

 the same time there is an increased flow of lymph from the lymphatics 

 of the neck. This increased flow of lymph does not depend upon a corre- 

 sponding increase in the rate of flow of the blood. In muscular work, 

 likewise, it may be shown that there is an increased formation of lymph. 



We must consider, here, an important discovery, namely, that there 

 are certain substances which incite the lymph flow. These are known as 

 lymphagogues, and are of two kinds. The lymphagogues of the first group 

 are obtained from the extracts of crab-muscles, blood-leeches, anodons, 



1 Asher and Barbera: Z. Biol. 36, 154 (1897); 37, 261 (1898); Asher and Gies: 

 ibid. 40, 180 (1900); Asher and Busch: ibid. 40, 333 (1900); Asher and Barbera: 

 Zentr. Physiol. 11, 403 (1897). 



