SOME MOOT POINTS 7.V XATURAL HISTORY. 255 



already elaborated matter for their support, and are not con- 

 tent, as it were, with the inorganic matters, such as the water, 

 mineral matters, etc., upon which the highest plants subsist 

 Distinctions which chemical science might be regarded as 

 having founded, and means of separating between animals 

 and plants which at the commencement of the present cen- 

 tury and even at a later date were regarded as of stable kind, 

 are seen to break down like weak evidence, when subjected 

 to the strict cross-examination of modern investigation. 



Turning next to the microscopist in search of definite 

 information respecting the boundary-lines between the two 

 kingdoms of living beings, we find that histology, or the 

 science which investigates the minute structure of bodies, 

 frankly owns its inability to solve the mystery of animal or 



D E I 



FIG. 39. Various cells, all highly magnified; A, a typical cell; B, cells from 

 cartilage ; c, from fat ; D, colour cell from frog's skin ; E, a plant-cell ; F and G, 

 nerve-cells ; H, a cartilage cell ; I, liver cells. 



plant-individuality. Thus, varied and different as the forms 

 of animals and plants appear to be, they present a striking 

 uniformity of structure and composition when resolved under 

 the scrutiny of the microscope into their constituent elements. 

 In the years 1837-38, the ideas which had previously been 

 growing upon microscopic observers regarding the composi- 

 tion of living bodies, took definite shape and appeared in 

 the form of the " cell-theory.'' This theory, supported in 

 the most direct manner by the accumulated observations of 



