16 OF VITAL MOTION. 



we suppose that the expansion of the latex will not 

 be commensurate with the change experienced by the 

 coats of the vessel ; and hence, the primary operation 

 of heat upon the vessel will be the production of a 

 vacuum between the coats and the contents. 



The operation of heat, therefore, may be the cause 

 of the primary act of absorption, for to fill the vacuum 

 which is thus formed, it is evident that there must be 

 a rushing inwards of aeriform or watery fluids from 

 neighbouring parts a phenomenon readily permitted 

 by the porosity, which is one of the properties of 

 organic membrane and thus the filling of the shrunk 

 and empty laticiferous web, on the return of spring, 

 may be nothing more than the necessary effect of the 

 increased warmth of the season. 



It does not appear, however, by what means the 

 solar heat can be concerned in the production of the 

 focal movements by which the latex is agitated, for 

 this agency operates uniformly and equally upon all 

 portions of the web. Nor in the construction of the 

 vessels themselves does there appear to be any pecu- 

 liarity which could localize the operation, inasmuch 

 as the focal points are subject to change, and not con- 

 fined to any fixed and permanent positions. At this 

 stage of our inquiry, also, we do not find any aid in 

 the physical agencies which are correlative of heat 

 namely, light, electricity, and the rest and therefore 

 we leave our present point of view, and proceed to 



