64i ANIMAL AND TEGETABLE MILK. 



hevea, I mixed a solution of carbonate of soda with the 

 milk of the papaw. No clot ig formed, even when pure 

 water is poured on a mixture of the milk with the alkaline 

 solution. The membranes appear only when, by adding an 

 acid, the soda is neutralized, and the acid is in excess. I 

 made the coagulum formed by nitric acid, the juice of 

 lemons, or hot water, likewise disappear by mixing it with 

 carbonate of soda. The sap again becomes milky and liquid, 

 as in its primitive state ; but this experiment succeeds only 

 when the coagulum has been recently formed. 



On comparing the milky juices of the papaw, the cow-tree, 

 and the hevea, there appears a striking analogy between the 

 juices which abound in caseous matter, and those in which 

 caoutchouc prevails. All the white and newly prepared 

 caoutchouc, as well as the waterproof cloaks, manufactured 

 in Spanish America by placing a layer of milk of hevea 

 between two pieces of cloth, exhale an animal and nauseat- 

 ing smell. This seems to indicate that the caoutchouc, in 

 coagulating, carries with it the caseum, which is perhaps 

 only an altered albumen. 



The produce of the bread-fruit tree can no more be 

 considered as bread than plantains before the state of 

 maturity, or the tuberous and amylaceous roots of the cas- 

 sava, the dioscorea, the Convolvulus batatas, and the potato. 

 The milk of the cow-tree contains, on the contrary, a 

 caseous matter, like the milk of mammiferous animals. 

 Advancing to more general considerations, we may regard, 

 with M. Gay-Lussac, the caoutchouc as the oily part, 

 the butter of vegetable milk. We find in the milk of 

 plants caseum and caoutchouc; in the milk of animals, 

 caseum and butter. The proportions of the two albuminous 

 and oily principles differ in the various species of animals 

 and of lactescent plants. In these last they are most fre- 

 quently mixed with other substances hurtful as food ; but of 

 which the separation might perhaps be obtained by chemical 

 processes. A vegetable milk becomes nourishing when it is 

 destitute of acrid and narcotic principles ; and abounds less 

 in caoutchouc than in caseous matter.* 



* The milk of the lactescent agarics has not been separately analysed ; 

 it contains an acrid principle in the Agaricus piperatus ? and in other 

 pecies it is sweet and harmless. The experiments of MM. Braconnofc, 



