Oil the Composition of the Blood. 
209 
3iri(l kldnpys, — in tlip one case as a chief constituent of tlie per- 
spiration, and in the other as that of the urine. 
Albumen exists in the serum at about the rate of 7 per cent. ; 
it maj rise a little above this, or sink as low as () per cent., con- 
sistent with health. In a plethoric habit of body there is a 
relative increase of the albumen ; and on the contrary, in a debi- 
litated condition, a diminished amount. The chief use of the 
•albumen is to form fibrine by a higher degiee of vitalization. 
Besides this, albumen is ccmsumed in the production of the gela- 
tine of the simple fibrous tissues, and in several of the secretions, 
as well as in the formation of those structures which are either 
epidermoid or homy. The source of the albumen is from the pro- 
tein compounds of the food, and its proper proportion in the se- 
rum is regulated by its constant consumption for the above-named 
purposes. The presence of this material is easily demtmstrated. 
Thus the addition of any mineral acid to the serum will throw 
<lown 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 
C(ualitative, but not a quantitative analysis of the serum, in so far 
as albumen is concerned, is thus obtained. A microscopic 
examination of solidified albumen does not, however, show that 
in acquiring this condition it has assumed any definite or struc- 
tural form. It is at most granular. 
It has already been stated that we possess no other means of 
obtaining serum except from coagulated blood. Nature, how- 
ever, can readily separate it in large quantities from the other 
constituents of the liquo)' sam/iiinis. We observe this under 
many circumstances, and frequently when an animal is in a weak 
and debilitated condition from disease. It is then that the serous 
part of the blood exudes through the capillary vessels and accumu- 
lates in the areolar tissue or in some of the great cavities of the 
body. The diseases which commonly pass under the term 
dropsy are especially referable to a cause of this kind. These 
effusions may differ, and even considerably so, from pure serum 
in the proportions of albumen and saline matters which they 
contain ; but nevertheless they are essentially of a serous nature, 
as is shown by their analyzation ; and as such they afford a 
proof that the serum is capable of being expelled from the living 
vessels apart from the other constituents of the blood. 
Salts of the Blood. — The saline matters of the blood are 
various, and are met with in the serum. They consist chiefly 
VOL. XXI. P 
