CHAP. III. FUNCTION OF NUTRITION. 21? 



effect. The viscosity of the milk alone renders it some- 

 what disagreeable. The negroes and free labourers 

 drink it, dipping into it their maize, or cassava bread." 

 Mr. Lockhart has subsequently afforded the following 

 additional particulars concerning this tree : " The 

 Palo de vaca is a tree of large dimensions. The one 

 that I procured the juice from had a trunk seven feet 

 in diameter, and it was one hundred feet from the root 

 to the first branch. The milk was obtained by making 

 a spiral incision into the bark. The milk is used by 

 the inhabitants wherever it is known. I drank a pint 

 of it without experiencing the least inconvenience. In 

 taste and consistence it much resembles sweet cream, 

 and possesses an agreeable smell." 



(204.) Receptacles for Milk. All the various milky 

 juices reside in the bark and leaves, and are not found 

 in the wood. They are contained in distinct receptacles, 

 and may be extracted by means of incisions chiefly 

 in the upper parts of plants, and which do not ex- 

 tend deeper than the bark ; otherwise they would be 

 diluted and impoverished by mixing with the as- 

 cending sap. M. Bertholet has recorded a remarkable 

 instance of the harmless quality of the sap in the 

 interior of a plant, whose bark is filled with a milky 

 proper juice of a poisonous nature. He describes the 

 natives of Teneriffe as being in the habit of removing 

 the bark from the Euphorbia canariensis, and then 

 sucking the inner portion of the stem in order to 

 quench their thirst, this part containing a consider- 

 able quantity of limpid and non-elaborated sap. The 

 reservoirs which contain the milky juice of the wild 

 lettuce (Lactuca virosa) are so remarkably irritable 

 that the slightest touch is sufficient to cause it to be 

 ejected from them with considerable force. When 

 this plant is about to flower, if an insect happens to 

 crawl over the surface of the stalk any where near its 

 summit a jet of milk is propelled. In general plants 

 which secrete these milky juices love the light; few 

 are found to affect shady situations, and none are aqua- 



