THE EFFECTS OF DE-NUTRITION. 703 



of the body, acts as a sort of spongy bed or matrix, into which the 

 residual part of the nutritive plasma escapes, and so may be more 

 easily taken up by the lymphatics which abound in it. 



Fourthly, the final residue of the exuded plasma, which is neither 

 used by the tissues of the body, nor absorbed by the intruded lym- 

 phatic vessels, remains to be accounted for. This must be conveyed, 

 probably, by simple and unavoidable dialysis, without power of selec- 

 tion or rejection, into the venous half of the capillary network, and 

 the minute venules immediately adjoining. No other destination can 

 be assigned to it, and unless it were carried off, dropsical accumula- 

 tions or effusions would take place in the tissues. From this it would 

 appear, that whilst the still serviceable parts of the residual plasma, 

 left after the nutrition of the other tissues, are restored indirectly to 

 the blood, by lymphatic absorption and assimilation, the unserviceable 

 or final, and no longer nutritious residuum, passes into the circulation 

 directly, by means of venous absorption. 



Lastly, with this final residuum of the nutritive plasma, there are 

 necessarily mingled the products of the disintegration of the tissues, 

 which always accompanies their action. Without waste there is no 

 use, and without use there is no life. It is the loss which living and 

 acting tissues undergo, which necessitates their nutrition ; and whilst 

 new pabulum is brought by the arterial blood, which yields a nutritive 

 plasma through the walls of the arterial half of the capillary network, 

 from which plasma all the tissues receive respectively their requisite 

 materials, the products of their waste would seem first to become dis- 

 solved in the ultimate residuum of the plasma, and with it, to enter 

 the venous blood through the walls of the venous half of the capilla- 

 ries and of the minute veins. These products of waste are really 

 effete, and no longer fit for the purposes of nutrition ; physiologically, 

 they are the result of a process of de-nutrition, and, chemically con- 

 sidered, of a process of oxidation of the tissue substance. It is these 

 which impart to the blood its positive venous characters. Thus, venous 

 blood is more watery; it contains less nutritive matter ; it is also 

 rendered impure by containing the waste products of the tissues, the 

 chief of which are carbonic acid, lactic acid, and urea. The former of 

 these, as we shall hereafter see, is replaced by oxygen in the lungs, 

 and so a negative defect in venous blood, the want of that stimulating 

 agent is supplied. Here, also, the carbonic acid is given off; whilst 

 the lactic acid, phosphates, and urea are eliminated, or cast out of the 

 blood by the excretory glands, especially by the skin and kidneys. 



The five stages of the nutritive process, though here separately de- 

 scribed, viz., the exudation of the nutritive plasma from the blood, the 

 assimilation of parts of this by the tissues under repair, the absorp- 

 tion and assimilation of other portions by the lymphatics, and lastly, 

 the re-absorption of the final residue, together with that of the waste 

 products of the tissues, by the venous capillaries and veins, are, of 

 course, in the living body, simultaneously arid continuously performed, 

 and in the healthy condition, with a perfect balance of action. Espe- 

 cially must the removal of the waste products be incessant, JOY they 



