225 



line 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, equally disappear by mixing it with car- 

 bonat of soda. The sap becomes milky and 

 liquid afresh, as in it's primitive state ; but this 

 experiment succeeds only when the coagulum 

 has been recently formed. 



In 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 the caout- 

 chouc prevails. All the white and newly pre- 

 pared caoutchouc, as well as the impermeable 

 cloaks, manufactured in Spanish America by 

 placing a layer of milk of hevea between two 

 pieces of cloth ; exhale an animal and nauseating 

 smell. This seems to indicate, that the caout- 

 chouc, 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 the plantains before 

 the state of maturity, or the tuberous and amy- 

 laceous roots of the cassava, the dioscorea, the 

 convolvulus batatas, and the potato. The milk 

 of the cow-tree contains, on the contrary, the ca- 

 seous matter, like the milk of mammiferous 



* See note B ; at the end of this book. 

 VOL. IV. Q 



