THE VOLATILE PART OF PLANTS. 103 



nation. It is not unlikely that vegetable casein may contain an admix- 

 ture of protagon (p. 93), or the products of its decomposition, from 

 which it is not easy to procure a separation. 



Mutual Relations of the Albuminoids. Some have 

 supposed that these bodies are identical in composition, 

 the differences among the analytical results being due to 

 foreign matters, and differ from each other in the same 

 way that cellulose and starch differ, viz. : on account of 

 different arrangement of the atoms. Others formerly 

 adopted the notion of Mulder, to the effect that the albu- 

 minoids are compounds of various proportions of hypothet- 

 ical sulphur and phosphorus compounds, with a common 

 ingredient, which he termed protein, (from the Greek sig- 

 nifying "to take the first place," because of the great 

 physiological importance of such a body.) Hence the 

 albuminoids are often called the protein-bodies. The trans- 

 formations which these substances are capable of under- 

 going, sufficiently show that they are closely related, with- 

 out, however, satisfactorily indicating in what manner. 



In the animal organism, the albuminoids of the food, of 

 whatever name, are dissolved in the gastric juice of the 

 stomach, and pass into the blood, where they form blood- 

 albumin and blood-fibrin. As the blood nourishes the 

 muscles, they are modified into flesh-fibrin, or entering the 

 lacteal system, are converted into casein, while in the ap- 

 propriate part of the circulation they are formed into the 

 albumin of the egg, or embryo. 



In the living plant, similar changes of place and of char- 

 acter occur among these substances. 



Finally, outside the organism the following transforma- 

 tions have been observed : Flesh-fibrin exposed while 

 moist to the air at a summer temperature for some days, 

 dissolves into a liquid ; if this liquid be heated to near 

 boiling, coagulation takes place, and the substance which 

 separates has the properties of albumin. On removing 

 the albumin and adding vinegar to the remaining liquid, 



