BLOOD AND LYMPH. 577 



from the liver and intestines of dogs, and from strawberry-extracts, etc. 

 In this case, the increased flow of the lymph can also be attributed to the 

 increased activity of an organ, the liver especially. On the other hand, it 

 has been assumed that these substances act upon the endothelium of the 

 capillaries in such a way that they are incited to increased activity. To 

 the lymphagogues of the second group belong sugar, urea, common salt, 

 etc. These cause an abundant lymph formation, whereby the plasma, 

 as well as the lymph, becomes more dilute. In this case also a specific 

 activity of the cells is presumed; here, that of the tissue cells. 



It is not difficult to understand that the work of organs increases the 

 production of lymph; for, on the one hand, the cells of the active organ 

 require an increased supply of nutriment, and, on the other hand, they 

 yield an increased amount of metabolic end-products. 



One might be tempted to ask why the presence of the lymph and the 

 liquid in the tissues is at all necessary, and why it would not be better to 

 have a more direct interchange between the blood and the cells of the 

 tissue. The utility of this arrangement is very clear; for, in the first 

 place, it is evident that by the interposition of a liquid which penetrates 

 into the smallest spaces between the tissues, it is made possible to effect a 

 more delicate exchange of material; and, on the other hand, it prevents 

 the cells from being over-supplied with nutriment at any one time; and, 

 furthermore, by this means it is possible to keep the composition of the 

 blood fairly constant, which would not be the case if the end-products of 

 the metabolism in an active organ were given up to the blood all at once. 

 The lymph also serves as a diluting medium. An observation of Asher 

 supports this view. He showed that normal lymph contains products 

 which, if directly introduced into the blood circulation, would give rise 

 to disturbances. If, for example, some of their own lymph from the neck 

 be injected into the internal carotid artery of dogs, changes are at once 

 produced in the blood pressure. 



The organism also has a means of protection in the so-called lymphatic 

 glands, or lymph-nodes, which are situated in the course of a lymph-vessel. 

 They have various functions. According to the way they are constructed, 

 it is easy to imagine that they, to a certain extent, act as filters and keep 

 back certain substances which are injurious to the body. It is also con- 

 ceivable that they are able to combine with substances which are given 

 up to the lymph in large amounts. They are constantly giving up leuco- 

 cytes, so that they in this way take part in the general metabolism. 



Closely related to the lymph are certain liquids which are secreted by 

 the serous membranes, which are provided with an endothelium and fulfil, 

 for the most part, purely mechanical functions. These liquids are called 

 transudates. Under normal conditions there is but a small amount of 

 these. They are deficient in formed elements. As regards the formation 



