PHYSIOLOGY OF CELLS. 129 



tions in the contents, such as thickening of the membrane with 

 laminated depositions, as in cartilage, and with the formation of 

 minute canals ; while within, also, the granules may be precipitated, 

 fat-drops, elementary vesicles, concretions, crystals, or nuclei may 

 be formed, and molecular movements may occur. 



The nuclei rarely participate in these changes, though they some- 

 times become clear in consequence of the liquefaction of their viscid 

 contents. Very rarely granules are developed in them ; and in cer- 

 tain animals, "urticating threads" and spermatozoids are developed 

 in nuclei. 1 



2. The process of secretion is manifested by cells in two ways: 

 First. Their contents consist of substances received from with- 

 out, unaltered, or slightly so; as in case of epithelium-cells, espe- 

 cially of serous membranes, and the cells of those glands which 

 simply separate certain substances from the blood e. g. the lachry- 

 mal glands and the kidneys. (Kb'lliker.) 



Secondly. The cell-contents include substances prepared within 

 the cell ; as the colored blood-corpuscles, fat-cells, the bile-cells in 

 the liver, and those (secreting the gastric fluid) of the gastric glands. 



3. Contraction is sometimes manifested by cell-membranes and by 

 the cell-contents. Contractile cell-membranes occur in many, if not 

 all, of the Protozoa, in the yolk-cells of the Planariae, in the heart- 

 cells of many embryos, &c. Some consider that the colorless cor- 

 puscles of man, the frog, and the skate, mucus-corpuscles, and the 

 cells in the meshes of the areolar tissue of the disk of the medusa, 

 are contractile cells. 2 



Contractile cell-contents are found in the fibre-cells of smooth 

 muscle, in the stellate cells of the skin of the embryo Umax, and in 

 striped muscular fibre. 



Certain important changes in the cell-contents occur in patholo- 

 gical conditions. Besides those already specified, the following may 

 be noted here : 



1. Fatty degeneration is the most common change in cell-contents, 

 more or less fat-drops accumulating in the cell. But it must be 

 borne in mind that the cells in certain parts and organs normally 

 contain a few fat-globules. 



1 Thus it is very certain that the molecular and chemical changes of the cell- 

 membrane and the nucleus are independent of each other. 



2 Bonders, however, maintains that the cell-contents only (and not the cell- 

 membrane) are contractile. 



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