82 MANUAL OF HISTOLOGY. 



action of fermenting matters in the cell-body, or to some properties inhe- 

 rent in the nucleus, seems natural. Thus, \ve see that the action of the 

 hepatic cell gives rise to the formation of the bile acids and glycogen. In 

 the gland-cells of the functionating mamma sugar of milk must be pro- 

 duced from some of the hydrocarbons it receives, or from albuminous 

 matters. In the cells of the salivary glands of the gastric and intestinal 

 follicles and of the pancreas, ferments are generated which do not exist 

 as such in the blood, and which impart to the secretions of the organs in 

 question their peculiar physiological properties. 



Now, these operations engaged in by the gland-elements are repeated 

 again in the proper or egotistical nutrition of individual animal cells. It 

 seems probable that in many cases constituents of the blood simply enter 

 animal cells in order perhaps after undergoing very slight modification 

 to become constituents of the latter. This is borne out by the fact that 

 the cells are principally built up, as it were, of albuminous compounds. 

 On the other hand, we frequently observe considerable transmutation to 

 take place, by means of which matters received acquire another nature. 

 Thus the protein compounds of laminated epithelium are converted gradu- 

 ally into keratin, the albuminous substances of other cells are transformed 

 into mucin, and again the fatty soaps of the blood assume the form of 

 neutral fats on entering the cells of adipose tissue a metamorphosis of 

 which but little farther is known. 



But the metamorphosis of matter taken up into the cell becomes espe- 

 cially striking in the case of the formation of pigments. Here we behold 

 the white blood-cell generating in its interior a colouring matter and be- 

 coming a red corpuscle ; in the same way granules of black pigment or 

 melanin are developed in the bodies of many originally colourless cells, 

 when they are known as pigment cells. 



The question as to what matters are generated by the cell itself, and 

 what are received into it from without already formed, is in many cases 

 difficult, and frequently impossible, to answer. 



Now, as to the retrograde metamorphosis of the components of the cell, 

 as to the liquefaction and discharge of the products of decomposition, we 

 know at present but very little. The most purely cellular tissues usually 

 exist in too small quantity to admit of chemical investigation. But occa- 

 sionally, under favourable circumstances, a few conclusions may be drawn 

 on these points. Thus the products of decomposition of striped muscle 

 may most probabty be regarded as similar to those of involuntary fibre, 

 judging from their chemical and morphological relationship ; and in the 

 contractile fibre-cell of the latter we suppose the albumen to be transformed 

 into kreatin, kreatinin, hypoxanthine, inosinic acid, inosite, and the 

 paralactic acid. 



In concluding this section, it may be remarked that Schwann has 

 designated those phenomena connected with the chemical transmutations 

 of the cell as " metabolic occurrences," and speaks of a " metabolic force" 

 inherent in cells. 



52. 



The interchange of material going on among animal cells, as a study, 

 (however scanty our knowledge of it may be), has made us acquainted with 

 the elaboration of amorphous matter, and with the excretion of fluids 

 containing the products of decomposition or the earlier substance of 

 cells in solution. It has also brought under notice a number of formations 



