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. 
Tn ‘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, 
