THE BLOOD. 155 
ical and its chemical composition, to what extent is not exactly 
known, when removed from the body. 
Composition of Serum.—The fluid remaining after coagulation 
of the blood can, of course, be examined chemically with con- 
siderable thoroughness and confidence. 
By far the greater part of serum consists of water; thus, it 
has been estimated that of 100 parts the following statement 
will represent fairly, well the proportional composition : 
Water. casters e Shoneds the ee eee os 90 parts ; 
Proteidse ss. es aes deve s ened seekers ae ie 8to9 “ 
Salines, fats, and extractives (small in 
quantity and not readily obtained 
TT GO) sis daranoare as aero eaeivae tae e vate 1 to 2 parts, 
The proteids are made up of two substances which can be 
distinguished by solubility, temperature at which coagulation 
occurs, etc., known as paraglobulin and serwm-albwmen, and 
which may exist in equal amount. 
It is not possible, of course, to say whether these substances 
exist as such in the living blood-plasma or not. 
The fais are very variable in quantity in serum, depend- 
ing on a corresponding variability in the plasma, in which 
they would be naturally found in greatest abundance after 
a meal. They exist as neutral stearin, palmitin, olein, and as 
soaps. 
The principal extractives found are urea, creatin, and allied 
bodies, sugar, and lactic acid. Serum in most animals contains 
more of sodium salts than the corpuscles, while the latter in 
man and some other mammals contain a preponderating quan- 
tity of potassium compounds. 
The principal salts of serum are sodium chloride, sodium bi- 
carbonate, sodium sulphate, and phosphate in smaller quantity, 
as also of calcium and magnesium phosphate, with rather more 
of potassium chloride. 
It is highly probable that this proportion also represents 
moderately well the composition of plasma, which is, of course, 
from a physiological point of view, the important matter. 
The Composition of the Corpuscles.—Taken together, the differ- 
ent forms of blood-cells make up from one third to nearly one 
half the weight of the blood, and of this the red corpuscles may 
be considered as constituting nearly the whole. 
The colorless cells are known to contain fats and glycogen, 
which, with salts, we may believe exist in the living cells, and, 
in addition to the proteids, into which protoplasm resolves it- 
