'£i 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 jibr in. 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 which 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 



C4o+H 31 +N 5 +Oi 3 . 

 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 



