148 CIRCULATING FLUIDS: 



elude that the act of nutrition is effected by the sole influence 

 of a vital power inherent in the cells, and that the plasma is 

 entirely passive. If the various tissues of the animal body, 

 different as they are in their chemical constitution, obtain 

 their nourishment from the protein- and fat- compounds of the 

 plasma (which contains the elements of the cells, but not the 

 different cellular substances themselves,) it is clear that the cells 

 and tissues must produce a metamorphic effect on that portion 

 of the nutriment which is homologous with themselves. Their 

 catalytic, or as Schwann 2, in his theory of cells, terms it, their 

 metabolic power, evolves from the plasma the materials that 

 serve for the nutrition of the cells. The plasma is here the cyto- 

 blastema, the catalytic or metabolic force lies in the cells and 

 tissues. But although the plasma acts only passively in this 

 nutritive process, Ave cannot deny it a peculiar vital power. This 

 is first manifested in the formation of the cytoblastema, for the 

 force that creates these forms cannot be regarded as inde- 

 pendent of the plasma. If the nucleus is formed by the so- 

 lidification of fibrin in the plasma, which from the similarity 

 of their constitution is probable, its formation must be re- 

 garded as the result of a purely plastic force in the liquor san- 

 guinis. If, however, all the different portions of tlie body, — 

 the muscles, bones, cartilages, horny matter, serous mem- 

 branes, sinews, neimlema, brain, &c., — are nourished and 

 formed by the protein- and fat-compounds of the plasma, 

 we must arrange these compounds into those which are, 

 and those which are not, homologous to the tissues. Neither 

 albumen, fibrin, nor fat can belong to the second division, 

 since the tissues are formed from these substances. 



I have already mentioned, that those constituents of the 

 plasma, that are excreted in the urine and the sweat, cannot 

 reasonably be considered as any longer nutritious, for it would 

 be at variance with our ideas of a consistent organization to 

 suppose that substances which could be subservient to the pre- 

 servation of the body should be removed from it ; it would be 

 just as irrational to conceive that they were conveyed into the 

 body in order to cu'culate therein, with the nutriment, with no 

 definite object; it only remains then for us to conclude that 



' Mikroskopische Untersuchuiigen, p. 231 and 234. 



