ANIMAL NATURE OF DIATOMEiE. 355 



elementary or primordial cells taken from beings respecting 

 whose animal or vegetable nature there can be no doubt. 

 If both these be subjected to the action of chemical 

 reagents, they manifest different results; hence we are 

 led to conclude that there exists a difference in their 

 chemical composition. 



It is useless to insist upon this mode of chemical 

 reasoning; it may suffice here to quote the results of 

 chemical researches. The nucleus is composed of a 

 quarternary azotised substance (0. H. C. A.) ; this applies 

 equally to an animal and a vegetable cell. The solid 

 tegument, again, of the animal cell is always a com- 

 bination of proteine with water, i. e. a quaternary azotised 

 substance also. (C.*° H.«^ O.'*' A.^) ; whilst that of the 

 vegetable cell always consists of an unazotised ternary 

 substance, isomeric with starch (C.^* H.^" 0.^°). The 

 contained liquid, also, is always ternary, unazotised in the 

 vegetable cell, quaternary and azotised in the animal. The 

 included solid substances are promiscuously ternary or 

 quaternary ; the former prevailing more in vegetables, the 

 latter in animals ; and among the former, chlorophyll (?) 

 starch, and gum are found exclusively in the vegetable 

 cell. Chemical reagents, too, disclose an essential pecu- 

 liarity in the vegetable cell. An extremely fine, thin 

 membrane, granular in structure, of a quaternary azotised 

 composition, like that of the nucleus, lines the inner wall, 

 and hence immediately surrounds all the contents of the 

 cell, including the nucleus, with which, in most instances, 

 it is in direct continuity. This fine membrane is so thin, 

 and adheres so closely to the inner wall, that, in order to 

 perceive it, we must resort to physical or chemical agents 

 to detach it. It exists in every cell, and precedes the 

 formation of the wall ; if it seem to be absent in any 

 case, the reason is that in most instances it soon 

 disappears. 



These are positive facts; and in most instances the 

 experiments by which they are confirmed admit neither 

 contradiction nor doubt. But in the special case of a 



