CHAP. I.] PROPERTIES OF TISSUES. 51 



cell-wall or nucleus into the ultimate elements of the tissues. The 

 cell- walls may be changed into a part, accessory to the complete 

 texture, as the sarcolemma or sheath of the muscular fibre ; but 

 the further organizing process takes place on its outer or inner 

 surface. And the nuclei, likewise, may be changed into parts, 

 which contribute to the nutrition of the tissue ; but not into its 

 essential elements. These, it must be remarked, are always the 

 product of an ulterior organizing process, connected chiefly with the 

 cell-wall. 



There seems reason to believe, that, during the organizing pro- 

 cess, which occurs simultaneously with the changes of the cell, a 

 chemical alteration takes place; for the cells of cartilage some- 

 times contain fat, and the cartilage of bone prior to ossification 

 contains chondrine, but, after the ossific process, gelatine is found : 

 and it is also stated, that the element which may be obtained from 

 the young cells of areolar tissue is pyine ; whereas gelatine is yielded 

 by the fully formed tissue. 



The formation of cells does not cease with the infancy of the 

 organism. These minute organic elements are most important 

 agents in various functions of the body at every period of its exist- 

 ence. By them the secretions are separated; and it is not im- 

 probable that they contribute largely to those changes in which 

 nutrition immediately consists. They are found floating in im- 

 mense numbers in the blood, as well as in the chyle and lymph ; 

 and, even in diseased secretions, as pus, they exist in great quan- 

 tity. In the inflammatory process, they are formed in great abun- 

 dance ; and in the malignant growths, which infest the body, so as 

 to manifest themselves at different parts of it, such as the various 

 forms of cancer, the same organic forms are to be found. 



In short, Schleiden and Schwann have proved that the nucleated 

 cell is the agent of most of the organic processes, whether in the 

 plant or animal, from the separation of the embryo from its pa- 

 rent, to the development, growth, and nutrition of the adult 

 individual. 



Properties of the Tissues. The fully grown tissues manifest 

 differences among themselves, not merely by their anatomical 

 characters, but by their properties. These may be conveniently 

 sub-divided into physical and vital. Strictly speaking, this is a 

 distinction without a difference ; for doubtless all the properties of 

 animal tissues maybe ascribed to the peculiar arrangement of their 

 particles, and arc, therefore, physical. Our reasons for adopting the 

 di\ision will appear in explaining the nature of these properties. 



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