108 HOW CROPS GROW. 



of hypothetical sulphur and phosphorus radicles with 

 a common ingredient, which he termed protein (from 

 the Greek signifying " to take the first place," because 

 of the great physiological importance of such a body). 

 Hence the designations protein-bodies and proteids. 

 The transformations which these substances are capable 

 of undergoing sufficiently show that they are closely 

 related, without, however, satisfactorily indicating in 

 what manner. 



In the animal organism, the albuminoids of the food, 

 of whatever name, are dissolved in the juices of the 

 digestive organs, and pass into the blood, where they 

 form blood albumin and globulin. As the blood nour- 

 ishes the muscles, they are modified into the flesh-albu- 

 minoids ; on entering the mammary system they are 

 converted into casein, while in the appropriate 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 

 character occur among these substances. 



The Albuminoids in Animal Nutrition. "\Ve step 

 aside fora moment from our proper plan to direct atten- 

 tion to the beautiful adaptation of this group of organic 

 substances to the nutrition of animals. Those bodies 

 which we have just noticed as the animal albuminoids, 

 together with others of similar composition, constitute 

 a large share of the healthy animal organism, and espec- 

 ially characterize its actual working machinery, being 

 essential ingredients of the muscles and cartilages, as 

 well as of the nerves and brain. They likewise exist 

 largely in the nutritive fluids of the animal in blood 

 and milk. So far as we know, the animal body has not 

 the power to produce a particle of albumin, or fibrin, or 

 casein except by the transformation of similar bodies pre- 

 sented to it from external sources. They are hence indis- 

 pensable ingredients of the food of animals, and were 



