OF ORGANIZED STRUCTURES IN GENERAL. 23 



is by gradually drawing to itself certain of these elements, that the 

 germ becomes developed into the complete fabric. Now, of the sixty- 

 two simple or elementary substances, which are known to occur in the 

 Mineral world, only about eighteen or nineteen are found in Plants and 

 Animals ; and many of these in extremely minute proportion. Some of 

 these appear to J)e merely introduced, to answer certain chemical or 

 mechanical purposes ; and the composition of the parts which possess 

 the highest vital endowments, is for the most part simpler and more 

 uniform. 



12. The actual tissues of Plants, when entirely freed from the sub- 

 stances they may contain, have been found to possess a very uniform 

 composition, and to agree in their chemical properties. The substance 

 which forms the principal part of the thickness of the walls of the cells, 

 vessels, &c., of which the Vegetable organism is composed, is identical 

 with /Starch in the proportion of its components ; but as these are in a 

 different state of aggregation, it is distinguished as Cellulose. It con- 

 sists of 12 Carbon, 10 Hydrogen, and 10 Oxygen ; or, in other words, 

 of Carbon united to the elements of water, in the proportion of eight 

 of the former to seven of the latter. It may be very easily converted 

 into gum or sugar, by chemical processes, which effect the removal or 

 the addition of the elements of water. Now there is no compound 

 known to exist in the Inorganic world, which bears the remotest analogy 

 to this ; and we have no reason to believe that it could be produced in 

 any other way, than by that peculiar combination of force which exists 

 in the growing Plant. But although Cellulose is the predominating 

 component of the Vegetable fabric, yet it is not the most essential ; for 

 late researches have shown, that within what has been ordinarily consi- 

 dered as the cell-wall, is a delicate membrane, termed the " primordial 

 utricle," which is really the original cell-wall, from the exterior of which 

 the layer of cellulose is secreted. And it is a very interesting fact, 

 that the composition of this membrane corresponds with that of the 

 proper cell-walls of the Animal tissues; it being, in fact, a proteine 

 compound ( 13). Hence every act of Vegetable growth involves the 

 production of this substance also, which is still more removed in its 

 composition from ordinary Inorganic compounds. 



L3. The composition of the Animal tissues, when freed from the 

 fluids they may contain, or from the solid matters which may have been 

 deposited within them, is nearly as uniform. We may distinguish 

 among them two chief proximate principles, which appear under various 

 modifications in a great variety of dissimilar parts, and which seem 

 capable of conversion into other principles by the addition or subtrac- 

 tion of some of their constituents. The first and most important of 

 these, named Proteine* consists of 40 Carbon, 31 Hydrogen, 5 Nitro- 

 gen, and 12 Oxygen ; and although its composition is so complex, it 

 appears to act like a simple body, in uniting with Oxygen, Acids, &c., 

 in definite proportions, as well as with Sulphur and Phosphorus ; with 



* Although it may be doubted whether Proteine has ever been actually obtained in a 

 separate state, yet the term maybe conveniently applied to that composite base, which 

 is united with different equivalents of sulphur and phosphorus in the albuminous com- 

 pounds. 



