22 
CASEIN AND PROTEIN. 
The three preceding substances, viz. albumen, fibrin and casein, are called proteine 
bodies ; protein itself being regarded as a mere modification of them. They exist ready 
formed in the juices of vegetables, and may each be separated by suitable methods. Thus, 
juices which are newly expressed, and allowed to stand a short time, will separate into 
two or more parts : one is a green gelatinous precipitate, which, when the coloring matter 
is removed, is a grayish white substance, and has been named vegetable fibrin. It sepa¬ 
rates from the juices, precisely as does the fibrin of the blood. So the clarified juices of 
all nutritive vegetables, among which we may enumerate asparagus, cauliflower, cabbage, 
turnip, oats and the various other kinds of grain, when boiled, produce a coagulum which 
is identical in composition with the serum of the blood, or the white of an egg : this is 
called vegetable albumen. In the leguminous vegetables, as peas, beans, etc., the other 
proximate element, casein, more particularly abounds. This, as has been already ob¬ 
served, forms a pellicle upon the top of the heated juices, and does not coagulate. 
These substances, too, I may add, are the chief constituents of the blood, and hence 
must be regarded as the proximate bodies which build up and form the basis of the animal 
frame. 
Protein is obtained from either albumen, fibrin or casein. In order to effect this, the 
substance must be well washed in succession with water, alcohol and ether, by which 
means the extractive matter, soluble salts and fats are removed. The phosphates of lime, 
and other salts insoluble in water, are removed by hydrochloric acid. Potash in solution 
in water, and moderately strong, dissolves the remaining earths, as well as the sulphur 
and phosphorus whiqh is usually present. The protein is then ready to be thrown down 
by acetic acid, which must be added in slight excess only. It is a gray gelatinous flocky 
substance, which must be washed from the acetate of potash upon a filter. When dried, 
it becomes hard and yellow. It is insoluble in water, alcohol or ether, and devoid of 
taste or smell. Its composition is represented by the formula 
C40-j- H31 -j- N5 -f- O12. 
Its symbol is Pr. It burns without leaving a residue. 
Protein may be obtained from most of the tissues or organs and fluids of organized bodies. 
Thus besides pure albumen, fibrin and casein, it may be obtained from hair, horn, and the 
crystalline lens of the eye. It is regarded by Mulder as the first product of organization : 
hence the term I am first; and it is regarded, of course, as the starting point of the tissues 
in the animal kingdom. The relations of protein to the acids need not be stated here : it 
is sufficient for my purpose to observe that it dissolves in dilute acids, especially the acetic 
and phosphoric. It is precipitated from them by tannin, absolute alcohol, ferrocyanide of 
potassium, etc. 
In regard to protein, I would, with great deference to the opinion of chemists, question 
the real existence of this body in the fluids or tissues in an insulated state, or one which 
exists independently of all other bodies. I do not question the product itself, or that such 
a product is readily obtained ; but that it is ever formed or found in the fluids or tissues as 
