VASO-CONSTRICTOR PROPERTY OF SHED BLOOD 



47 



be looked upon as a form of ' first aid ' to diminish the haemor- 

 rhage, and also to make it less easy for the beginning clot to be 

 washed away. It is obvious that the two processes would be 

 mutually advantageous in dealing with those injuries of the vascular 

 system on the prompt repair of which the very existence of the 



Fig. 9. Frog Perfusion Experiment with Serum. Curves showing the flow. The 

 number of drops per half-minute is laid off along the vertical axis, and the time 

 (in half-minutes) along the horizontal axis; 38 drops correspond to i c.c. 



organism at all times depends, and it is not without interest to 

 find that special formed elements in the blood, the platelets, are 

 pre-eminently associated with both processes. 



SECTION III. THE CHEMICAL COMPOSITION OF BLOOD. 



The serum of coagulated blood represents the plasma minus 

 fibrinogen; the clot represents the corpuscles plus fibrin. Thus: 



Plasma - Fibrin (o gen) = Serum. 



Corpuscles + Fibrin = Clot. 



Plasma + Corpuscles Serum +Clot 



Blood. 



Bulky as the clot is, the quantity of fibrin is trifling (0-2 to 0-4 per 

 cent, in human blood). The plasma contains about 10 per cent, 

 of solids, the red corpuscles about 40 per cent., the entire blood 

 about 20 per cent. 



Serum contains 7 to 8 per cent, of proteins, about 0-8 per cent, 

 of inorganic salts, and small quantities of neutral fats, soaps, 

 cholesterin esters, lecithin, dextrose, urea, lactic acid, glycuronic 



acid, amino - acids, 



Solids 



Cor/7usdes[~ 



and other sub- 

 stances. The chief 

 proteins are serum- 

 albumin and serum- 

 globulin. In the rab- 

 bit the former, in 

 the horse the latter, is the more abundant ; in man they exist in not 

 far from equal amount. A small quantity of nucleo -protein and of 

 fibrino-globulin (which some consider a soluble product formed from 



Plasm* 



Fig. 10. Diagram showing Relative Quantity of Solids 

 and Water in Red Corpuscles and Plasma. 



