REMARKS ON COMPOSITION OF THE BLOOD. 609 
specific gravity varies from about 1*025 to 1*050. It is a 
very important element of the blood, containing not only 
the water and saline materials of that fluid, but also the albu¬ 
minous matters in a state of free solution. In short, it may 
be said to include the principal portion of all the consti¬ 
tuents of the blood with the exception of the fibrine, the 
haematine, the globuline, and the cells. The proportion which 
its several parts bear to each other will materially depend on 
certain conditional circumstances, such as the kind of food 
on which an animal is fed, the state of its health, the uses 
to which it is put, the temperature to which it is exposed, 
&c. Notwithstanding these disturbing causes, if the vital 
forces are still active, the balance is fairly maintained. Thus, 
speaking in general terms, every 1000 parts of serum contain 
about 780 of Mater; and although this proportion, even in 
health, is subject to variation, and may sometimes rise to 790 or 
sink to 700, the first-named quantity is nevertheless present 
as a rule. Any diminution in the amount of water is quickly 
compensated for by the thirst which it creates, while any 
excess will be as rapidly removed by the skin and kidneys,— 
in the one case as a chief constituent of the perspiration, 
and in the other as that of the urine. 
Albumen exists in the serum at about the rate of 7 per 
cent.; it may rise a little above this, or sink as low as 6 per 
cent., consistent with health. In a plethoric habit of body 
there is a relative increase of the albumen; and on the con¬ 
trary, in a debilitated condition, a diminished amount. The 
chief use of the albumen is to form fibrine by a higher degree 
of vitalization. Besides this, albumen is consumed in the 
production of the gelatine of the simple fibrous tissues, and in 
several of the secretions, as well as in the formation of those 
structures M 7 hich are either eperdermoid or horny. The 
source of the albumen is from the protein compounds of the 
food, and its proper proportion in the serum is regulated by 
its constant consumption for the above-named purposes. The 
presence of this material is easily demonstrated. Thus the 
addition of any mineral acid to the serum will throw doM r n the 
albumen in the form of a dense white precipitate ; or if the 
serum be exposed to heat, the coagulation of its albumen will 
take place. A temperature of about 165° of Fahrenheit will 
generally be required for this purpose, unless an unusually 
large amount is present, when a lower temperature will suffice. 
If, however, the albumen exists in a less than usual quantity, 
a much higher temperature will be required to effect its 
coagulation. A qualitative, but not a quantitative analysis 
of the serum, in so far as albumen is concerned, is thus 
