BLOOD. 199 



the act of circulation must necessarily be this : there must be 

 a substitution of fresh and proper nutriment to supply the 

 place of those constituents of the blood which are being perpe- 

 tually consumed ; for it is obvious that if in each circulation 

 the consumption of albumen or ha^matoglobulin exceeded the 

 supply by the merest trace, after a certain period the blood 

 would acquire an abnormal constitution. We know that al- 

 bumen, fibrin, and salts are consumed in the nutrition of the 

 peripheral system ; if therefore the blood receives no fresh 

 supply of these substances, before it arrives in the larger 

 venous trunks, it is clear that the venous blood must be poorer 

 in these substances than the arterial. 



The blood also conveys away from the peripheral system 

 various products formed by the consumption of the tissues ; for 

 instance, certain salts, extractive matters, &c., some of which 

 are eliminated by the kidneys, in a state of great dilution, 

 while others ai'e removed by the skin. If the quantity removed 

 exceed the supply, the venous blood will be poorer in ex- 

 tractive matters and salts than the arterial ; it will be richer 

 in these substances if the reverse be the case. 



The venous blood will contain more or less water than the 

 arterial, according as the elimination of water by the kidneys, 

 liver, skin, and lungs, exceeds or is less than the quantity 

 supplied by the fluid of nutrition. 



The blood-corpuscles, and the germs from which they are 

 developed, are hkewise supplied to the blood by the nutrient 

 fluids. They are further developed, and ultimately dissolved 

 during the course of the circulation, and their development 

 and solution is especially facilitated at those points where the 

 action of oxygen on the blood is the most powerful. 



It is obvious that the blood, immediately after having re- 

 ceived the chyle, must contain more blood-corpuscles than 

 before ; it depends however upon several circumstances whe- 

 ther venous generally contains more or less corpuscles than 

 arterial blood. 



The plasma receives a supply of fibrin from the solution of 

 the blood-corpuscles ; if the supply exceeds the consumption of 

 this constituent in the peripheral system, the venous blood 

 may become richer in fibrin than the arterial. 



If any albumen should be produced by the solution of the 



