984 SPECIAL PHYSIOLOGY. 



sition. It may be structureless, striated, fibrillated, fibrous, distinctly 

 granular, or organically crystalline. Lastly, cells may undergo atro- 

 phy, or degenerate, become the seat of morbid deposits, especially of 

 fat, and may finally die. 



In contrasting the animal with the vegetable cell, it may be said 

 that each vegetable cell, always a cystoplast, retains its own cell-wall, 

 and is, in a certain sense, independent of the rest. The intermediate 

 substance is either absent or invisible, or it takes the form of a sepa- 

 rate periplast for every cell. Each cell is incased anatomically, and 

 isolated physiologically. They cohere rather than co-operate. 



As to the animal cells, they are sometimes cystoplasts, often gym- 

 iioplasts. The presence of a separate periplast is not universal ; the 

 endoplast, probably, has not even a primordial utricle ; the outlying 

 region of the cell is not specially protected, but the intermediate 

 matrix, which may be a common periplast, is most abundant, and often 

 curiously specialized in structure and composition. The cells are 

 fused together rather than coherent, and they manifest great depend- 

 ence on each other, less individual isolation of function, and more 

 marked physiological co-operation. 



Nevertheless, both animal and vegetable cells are organic bodies, 

 living by the properties operating in their centres of growth and nu- 

 trition, the nucleus or nucleolus. The vegetable cell feeds upon inor- 

 ganic materials, the animal cell on a pabulum of organic origin, but 

 not on an organized pabulum. Organization only exists when, under 

 the influence of nuclear, nucleolar, or cell action, the nutrient pabulum 

 forms part of a living cell or its contents. 



Development of the several Tissues. 



Connective Tissue, and its varieties, areolar, fibrous, and jelly-like. 



The embryonal connective tissue is a jelly-like substance, consisting of a 

 transparent, soft, amorphous matrix, in which numerous nucleated cell-ele- 

 ments are found. According to one view, some of these cells elongate in the 

 soft matrix, become fusiform, unite into long wavy bands, and then split into 

 the fibrillse of the fibrous or areolar forms of connective tissue, their nuclei 

 being ultimately lost sight of. According to another explanation, the elon- 

 gated cells and the matrix blend together into a homogeneous mass, which 

 then becomes fibrillated, Fig. 122, d. In any case the nuclei remain as con- 

 nective tissue corpuscles. In many situations, softish and nearly homogeneous 

 tissues are met with, which are evidently modifications or arrested develop- 

 ments of connective tissue, as in the coats of small vessels, in the soft neu- 

 rilemma of the smallest branches of nerves, in the submucous coat and villi 

 of the small intestine, in the papillae of the skin, and elsewhere. The cornea 

 presents a peculiar form of fibrous connective tissue ; whilst the vitreous hu- 

 mor is an imperfectly developed areolar tissue, in which the cells have gradu- 

 ally disappeared, or exist only at the surface, whilst the matrix has become 

 deliquescent. The soft embryonal connective tissue ami the vitreous humor 

 contain no gelatin, but merely albumen and mucin. The chemical change 

 into gelatin occurs only with the perfect development of this tissue. The 

 cornea contains chondrin, and not gelatin. 



