190 ON THE MILK-SAP 



(Juss.), and the Nettle plants, are distinguished by a 

 peculiar anatomical structure. In their bark, and also 

 partly in their pith, we find a quantity of long, variously 

 curved and branched tubes, which are not unlike the veins 

 of animals. Through this similarity, Professor Schultze, 

 of Berlin, was led to develop a comprehensive theory of 

 a circulation through these structures of the fluids con- 

 tained in them, which he called vital juices, which theory, 

 unhappily, cautious science was compelled immediately upon 

 its promulgation, which made so great a show, that it 

 appeared as one of the treatises honoured by the Paris 

 Academy with the Monthyon prize, to demonstrate to 

 be a mere brain-spun phantom. In these tubes we find 

 a thick juice of the consistence of very rich milk, whence 

 it is called milk-sap. Its colour is usually milk-white, but 

 yellow, red and, very rarely, blue milk -saps are met with, 

 but more frequently still they are wholly colourless. Like 

 animal milk, this juice consists of a colourless fluid and 

 small globules. The composition displays the most varied 

 constituents, and upon the variation of quantity and modes 

 of mixture of these matters, depend the abundant varieties 

 of this juice. All contain more or less Caoutchouc, which 

 occurs in the form of little globules. These are prevented 

 from coalescing by an albuminous substance, in the same 

 way as are the butter globules in milk. Exactly like the 

 cream (the butter) in milk, the Caoutchouc globules rise to 

 the surface of the milk-sap of plants when left to stand, 

 here form a cream and coalesce, and cannot, any more 

 than butter, be separated again into their distinct globules. 

 All those three great families which are distinguished by 

 their abundance of milk-sap, although differing very widely 

 botanicaliy, exhibit some most remarkable agreements 

 through the nature of their milk-sap. 



