ELEMENTARY FORMS OF ORGANIC STRUCTURE. 119 



CHAPTER III. 



OF THE STRUCTURAL ELEMENTS OF THE HUMAN BODY, AND THE 

 VITAL ACTIONS WHICH THEY EXHIBIT. 



97. IT may be stated, as one of the most general facts in Physiology, that 

 Vital force can only manifest itself through that peculiar arrangement of mat- 

 ter, which is distinguished as organized structure;* since this alone affords that 

 assemblage of material conditions, which is required to concur with the dynam- 

 ical agency that is the active principle of the whole, for the production of the 

 phenomena of Life. (See INTRODUCTION, p. 36.) But of such organized struc- 

 ture, there are a ^reat many varieties, even within the single organism of Man. 

 Thus it has been customary to reckon as the distinct structural components, or 

 Elementary Tissues of which his fabric is composed, Bones, Teeth, and Carti- 

 lages, which form its solid framework, with the Ligaments which unite these 

 to each other, and the Tendons which communicate motion to them from the 

 muscles ; the Skin (with its appendages) which envelops the exterior of the 

 body, the Mucous Membranes which are prolonged from this into all the cavi- 

 ties that are connected with its surface, and the Serous Membranes which line 

 the shut sacs ; the Bloodvessels and Absorbents, which serve for the distribu- 

 tion of the nutritious fluids, and the Glands which eliminate various substances 

 from these ; the Muscles which communicate motion to the osseous framework, 

 or to the contents of the canals and tubules that convey alimentary and other 

 substances through the system, and the Nerves which excite the Muscles to 

 contraction and also serve as the instruments for the reception of sensations and 

 for the operations of the mind and finally, the Areolar tissue which serves to 

 connect together the preceding, and the Adipose which is commonly diffused, 

 more or less universally, through this, but sometimes forms masses of its own ; 

 each of these having a structure and a mode of vital action in some degree 

 peculiar to itself, and being hence considered as possessing distinctive vital en- 

 dowments. In attempting, therefore, to analyze the varied and complex pheno- 

 mena which make up the physiological history of Man, there is an obvious 

 advantage in first making ourselves acquainted with these elementary compo- 

 nents of his corporeal structure, and with the several forms of vital activity to 

 which they minister. But, although, by so doing, we might seem to have com- 

 menced with the very foundations of Physiological Science, yet such is not 

 really the case ; for before considering what are the peculiar distinctions in 

 structural arrangement and in vital properties, which these tissues severally ex- 

 hibit, we should inquire what they all have in common, and should seek to de- 

 termine whether there be any fundamental relation between their respective 

 types of organization and modes of vital activity, which is capable of being em- 

 bodied in a general expression. And this inquiry has a value at the present 

 time, to which it could never before lay claim ; since, on the one hand, the 

 microscopic examination of the Elementary Tissues, not only in their complete 

 state, but also in their various phases of development, has shown that they have 



1 For the distinctive characters of Organized Structures in general, see the Author's 

 "Principles of Physiology, General and Comparative," CHAP, n., Am. Ed. 



