THE COMPOSITION OF BLOOD-SERUM. 183 



plasma. What the plasma contains we may learn by ex- 

 amining blood-serum, which is plasma minus fibrin. 



Blood-serum is very different from water; if we keep on 

 boiling pure water in a saucepan it will all go off in steam 

 and leave nothing behind, but if we try to boil serum we 

 find that we cannot do it; before it gets as hot as boiling 

 water it sets into a stiff, solid mass just like the white of a 

 hard-boiled egg. In fact the serum contains dissolved in it 

 an albumen which is very like that in the white of an egg, 

 and is coagulated in the same way by boiling. About eight 

 and a half pounds of albuminous substances exist in one 

 hundred pounds of blood. 



Blood-serum also contains considerable quantities of oily 

 and fatty matters, a little sugar, some common salt and 

 carbonate of soda, and small quantities of very many other 

 things, chiefly waste products from the various tissues. 

 Nine tenths of the blood-plasma are water. 



Composition of the Red Corpuscles. In the fresh moist 

 state these contain a little more than half their weight of 

 water. Nine-tenths of their solid part is haemoglobin ; 

 they also contain phosphorus and iron and potassium. 



The Blood Gases. Ordinary fresh or salt water has a 

 good deal of air dissolved in it, which fishes breathe. Blood 

 also contains a quantity of gases which it gives off when 

 exposed to a vacuum, about sixty pints of gas to a hundred 



What may we learn by examining blood-serum? What is blood- 

 serum? 



What happens when we try to boil blood-serum? Why does it 

 coagulate in heating? What proportion of albumen exists in blood? 



What things are found in the blood-serum in addition to water? 

 JIow much water is there in ten pints of blood-plasma? 



How much solids do the red corpuscles contain? What propor- 

 tion of these is haemoglobin? Name other things found in the red 

 corpuscles. 



What do fishes breathe? What does blood give off when placed in 

 a vacuum? How many pints of gas for each ten of blood? 



