166 



ACADEMIC BOTANY. 



it; they appropriate its nitrogen, which enters the pabu- 

 lum and is carried up to the 

 Jeaves. There it is mixed 

 with oxygen, hydrogen, and 

 carbon ; the four elements, — 

 Oxygen, Hydrogen, Carbon, 

 Nitrogen, — acted upon by sun- 

 light and chlorophyl, form 

 Protoplasm, which is a qua- 

 ternary oompownd. It makes 

 the Caseine in the curd . of 

 milk; Gelatine in bones; Fi- 

 brine in flesh and muscles. 

 The Gluten in Wheat and the 

 Legumine in Beans represent 

 it ; it gives their best value to 

 our grains as food. Its quan- 

 tity is usually small in propor- 

 tion to the other constituents. 



Fig. 237. — West Indian Papaw {Carica 

 Papaya) ; plant in fruit, with separate (f 

 and $ fls. 



408. Pibrine was supposed to be 

 exclusively an animal fabric until 

 its discovery in the "West Indian 

 Papaya (Pig. 237) by the eminent 

 French chemist Vauquelin. It exists 



in the juices of the Papaya in great abundance, and has the property 



of making the toughest meats tender. 



The exhalations produce the same effect 



when meats are suspended from the tree 



or wrapped in its leaves. If old animals 



are fed on the fruit or leaves, their flesh 



becomes tender when cooked soon after 



slaughtering ; left raw, however, it spoils 



rapidly. Still more remarkable is theCow- 



tree of South America (Pig. 238), which 



yields milk of the same constituents as 



that of a cow, and of as good quality. 



It has the taste of sweet cream, and an 



agreeable, balsamic fragrance. A cheesy 



.=cum, like cream, rises on it, and in a 



few days it sours and putrefies like ani- 

 mal millc. The tree grows to the 



height of 100 feet, with a diameter of 6 



feet, its shaft 60 to 70 feet long below 



the first branches. It forms great for- 

 ests on the mountains near the sea-coast 



of Venezuela. The trees are milked daily, by incisions made in the 



Cow-tree (GdlactoUeit- 



