702 SPECIAL PHYSIOLOGY. 



By this, the nerve tissue attracts from the plasma outside the capilla- 

 ries its essential fatty and other constituents, the muscular fibre 

 assumes the materials for fresh syntonin, the cartilage those for its 

 chondrin, the bones their peculiar animal and earthy materials, and so 

 on of every other tissue of the body. The act of nutritive assimila- 

 tion is said to imply a metabolic effort, operating in regard to the sub- 

 stance of the tissues, whilst in development or evolution, this is asso- 

 ciated with a metamorphic effort, which determines their form. Both 

 kinds of nutritive phenomena are manifest chiefly, probably exclu- 

 sively, in certain areas around the nuclei, or corpuscles, of the cells, 

 the so-called germinal centres, which are therefore known as areas 

 and centres of nutrition. The few cases in which, as in elastic liga- 

 ments, the nuclei or corpuscles are said to be absorbed, may only be 

 apparent exceptions to the rule. Certain conditions of the blood, and 

 of the temperature of the body, are essential to the occurrence of 

 nutritive actions. They are most active at the commencement of the 

 life of any animal, and gradually decline, as that advances, until the 

 power to maintain the body is overcome by the forces which lead to 

 its degeneration and decay. 



In reference to the act of assimilation, and, indeed, of original organization, 

 it is remarked by Graham, that colloidal substances may not only be regarded 

 as forming the essential plastic elements of the body, capable, like all colloids, 

 of existing both in the liquid and in the pectous condition; but that, in the 

 organizing and assimilating process, these colloidal bodies do pass from the 

 liquid into the pectous state, as they assume the form and characters of tissues 

 and organs. The slow rate of these colloidal changes harmonizes with the 

 gradual and periodic nature of the processes of growth and disintegration, 

 with which all vital phenomena, whether of vegetative or animal life, are con- 

 nected. The ENERGIA, or force, peculiar to colloids, may be, indeed, the pri- 

 mary source of the physical force appearing in the phenomena of vitality 

 (Graham). 



Thirdly, the result of the act of assimilation by the various tissues, 

 is to leave a residual fluid in the interspaces of the tissue-elements, 

 outside the capillary vessels. The nature of this interstitial fluid, 

 unlike the common plasma, of which it is a residue, must differ in the 

 different tissues, as, for example, in muscle, brain, liver, and connec- 

 tive tisssue. This residual portion of the nutritive plasma not being 

 effete, but merely defective in composition, is supposed to enter the 

 commencing lymphatics, and thus to be returned to the blood through 

 the absorbent system. Probably, as already indicated, this is accom- 

 plished by true assimilative acts on the part of the lymphatic vessels 

 and glands, owing to which certain appropriate constituents, only, of 

 the residual portion of the plasma enter the commencing lymphatics. 

 It is remarkable that these vessels are most abundant in the connec- 

 tive tissue, in which the residual part of the plasma is least altered, and 

 few or absent in muscle and brain, where the greatest modifications are 

 effected in it, and where, accordingly, it is less fitted to form fresh 

 lymph. It might be conceived, without adopting Virchow's and Reck- 

 linghauser's views as to the origin of the lymphatics in the connective 

 tissue corpuscles, that the areolar tissue in, and between, all the organs 



