120 OF THE STRUCTURAL ELEMENTS OF THE HUMAN BODY. 



far more of similarity in intimate structure, as well as a closer community of 

 origin, than could have been even suspected without such scrutiny ; whilst, on 

 the other, the clearer apprehension to which we have been led by the progress 

 of Physical Philosophy, 1 in regard to the relations of different modes of Dynami- 

 cal agency, seems to render it possible to attain to a far more definite and compre- 

 hensive view than was previously within our reach, in regard to the nature of Vital 

 Force, and the conditions of its operation. Of the existence of this force, we 

 have just as much evidence in the phenomena exhibited by living beings, as we 

 have of the force of Gravitation in determining the movements of the heavenly 

 bodies, or of that of Chemical Affinity in producing changes of combination 

 among the elements of our own planet. But the peculiar complexity of the 

 circumstances under which it operates, and the co-operation of Chemical and 

 Physical agencies in many of the phenomena which essentially depend upon it, 

 frequently obstruct the recognition of its acts, and constitute an additional rea- 

 son for studying these under their simplest forms. 



1. Of the Elementary Forms of Organic Structure, and their Modes of Vital 



Activity. 



98. All the Elementary Tissues seem reducible, by Microscopic analysis, to 

 three primitive forms ; namely, Cells, Fibres, and Membranes. Of these it 

 is obvious that Cells are the most essential j since in the entire Vegetable king- 

 dom, as well as in the lowest tribes of Animals, the whole fabric is composed of 

 cells and their derivatives ; and there is a period in the history of even the 

 Human organism, when neither of the other elements exists. We shall find, 

 moreover, that it is by cells and their derivatives, that all the proper vital 

 actions of the body are performed. To these elements, however, Fibres? are 

 added in the bodies of the higher animals ; for the sole purpose, apparently, of 

 conferring upon their parts that freedom of movement which is essential to the 

 conditions of Animal existence. There is every reason to believe, that their 

 function is purely physical ; being nothing else than the resistance to tension 

 (with or without a certain degree of elasticity), of which advantage is taken in 

 two principal modes; such fibres being used to bind together separate parts that 

 are to have a certain range of motion one upon the other, and also to communi- 

 cate and apply mechanical power generated at some other and (it may be) dis- 

 tant point. The simple homogeneous Membrane, also, which is known as 

 "primary" or " basement-membrane," must be considered as one of the less 

 essential among the fundamental constituents of the Human organism ; though 

 its office is still of great importance. As regards the vital functions, simple 

 membrane may be considered as entirely passive ; but it serves the very im- 

 portant physical purpose of limiting and bounding the tissues of various organs, 

 and of separating the various collections of fluid within the body, in such a 

 manner as to prevent their too ready admixture, whilst admitting a certain 

 amount of transudation from one to the other. We shall now consider each of 

 these Elements in more detail. 



99. Of Cells, and Cell-Life. The Cells which are thus to be regarded as 

 the fundamental components of the Animal body, differ in no important par- 

 ticular of structure or composition, from those of which the Vegetable fabric is 

 made up ; and their endowments also may be shown to be essentially similar, 



See especially Prof. Grove's Treatise on "The Correlation of the Physical Forces." 

 2 This term is here used in the strict sense, as applicable to the solid and simple fibres 

 of which Ligaments, Tendons, &c. are made up, and not to the (so-called) Muscular and 

 Nervous fibres, which, as will hereafter appear, are really tubes consisting of elongated or 

 coalesced cells. 



