88 THE BLOOD. 



corpuscles. Its principal constituent is albumen, of which 

 it contains about 8 per cent., and the coagulation of which, 

 when heated, converts nearly the whole of the serum into 

 a solid mass. The liquid which remains uncoagulated, 

 and which is often enclosed in little cavities in the coagu- 

 lated serum, is called serosity : it contains, dissolved in 

 water, fatty, extractive, and saline matters. 



Variations in the principal Constituents of the Liquor Sanguinis. 



The water of the Hood is subject to hourly variations in its 

 quantity, according to the period since the taking of food, 

 the amount of bodily exercise, the state of the atmosphere, 

 and all the other events that may affect either the ingestion 

 or the excretion of fluids. According to these conditions, 

 it may vary from 700 to 790 parts in the thousand. Yet 

 uniformity is on the whole maintained ; because nearly 

 all those things which tend to lower the proportion of water 

 in the blood, such as active exercise, or the addition of 

 saline and other solid matter, excite thirst ; while, on the 

 other hand, the addition of an excess of water to the blood 

 is quickly followed by its more copious excretion in sweat 

 and urine. And these means for adjusting the proportion 

 of the water find their purpose in maintaining certain im- 

 portant physical conditions in the blood ; such as its proper 

 viscidity, and the degree of its adhesion to the vessels 

 through which it ought to flow with the least possible 

 resistance from friction. On this also depends, in great 

 measure, the activity of absorption by the blood-vessels, 

 into which no fluids will quickly penetrate, but such as are 

 of less density than the blood. Again, the quantity of 

 water in the blood determines chiefly its volume, and 

 thereby the fulness and tension of the vessels and the 

 quantity of fluid that will exude from them to keep the 

 tissues moist. Finally, the water is the general solvent of 

 all the other materials of the liquor sanguinis. 



