THE BLOOD AND THE LYMPH 



271 



of the oxygen and nutrients inward from the blood-capillaries, and on the 

 other hand that in the path of the carbon dioxide, water, sarcolactic 

 acid, and other excreta outward from the varied tissue-protoplasm into 

 the blood-capillaries. 



THE FORMATION OF LYMPH. It is as important as it is difficult to 

 fully realize how intimately related are the lymph and the blood. Indeed, 

 as we have seen, the former is almost a diluted filtrate of the latter, a 

 trifle richer in products of the tissues' waste, containing more water, only 

 by accident any erythrocytes, and a much smaller proportion of proteids. 



FIG. 143 



Production of protrypsinogen 



(enzyme). 

 New erythrocytes. 



Destruction of erythrocytes. 

 Production of uric acid. 

 Lymphocytes. 



Some theories as to the functions of the spleen. The arrows suggest five of the uses that 

 have been proposed for this however still mysterious organ. Smooth muscle is present in the 

 spleen, but what its motor purpose in the circulation is it would be at present hard to define. 



It is, however, very variable (according to the metabolism) in all its 

 components. Over and over again it has been shown experimentally 

 that when crystalloids (freely osmosible, soluble substances) are in- 

 jected into the circulation, the elapsed time before they appear in the 

 lymph is inappreciable. In other words (and this cannot be too well 

 understood), the whole body is largely liquid, and especially so is the 

 endothelium of the blood-capillaries and lymphatics. The blood at a 

 rapid rate circulates through almost every minute portion of the organism 

 and makes a circuit so quickly and so often that, with the blood-capillaries 



