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of the colour of the yolk of an egg ; they enlarge 

 as if by the prolongation of divergent fibres. 

 The whole liquid assumes at first the appearance 

 of an agate with milky clouds ; and it seems as 

 if organic membranes were forming under the 

 eye of the observer. When the coagulum extends 

 to the whole mass, the yellow spots again dis- 

 appear. By agitation it becomes granulous like 

 soft cheese *. The yellow colour reappears on 

 adding afresh a few drops of nitric acid. The 

 acid acts in this instance as the oxygen of the 

 atmosphere at a temperature from 27° to 35° ; 

 for the white coagulum grows yellow in two or 

 three minutes, when exposed to the Sun. After 



* The substance which falls down in grumes and filamen- 

 tous clods is not pure caoutchouc, but perhaps a mixture of 

 this substance with caseum and albumen. Acids precipitate 

 the caoutchouc from the milky juice of the euphorbiums, fig- 

 trees, and hevea ; they precipitate the cascwm from the milk 

 of animals. A white coagulum was formed in vials closely 

 stopped, containing the milk of the hevea, and preserved 

 among our collections, during our journey to the Oroonoko. 

 It is perhaps the developement of a vegetable acid, that then 

 furnishes oxygen to the albumen. The formation of the 

 coagulum of the hevea, or of a real caoutchouc, is nevertheless 

 much more rapid in contact with the air. The absorption of 

 atmospheric oxygen is not in the least necessary to the produc- 

 tion of butter, which exists already formed in the milk of 

 animals ; but I believe it cannot be doubted, that, in the 

 milk of plants, this absorption produces the pellicles of 

 caoutchouc, of coagulated albumen, and of caseum, which 

 are successively formed in vessels exposed to the open air. 



