ELEMENTS OF STRUCTURE. 



95 



distributed throughout the system, and which constitute the normal 

 contents of the cells of other tissues. These are (1), neutral fats, deposits 

 of which, for instance, cause the destruction of nume- 

 rous cells of the Graafian follicle during the forma- 

 tion of the corpus luteum in the ovary (fig. 95. a). 

 The same effect is produced by these fats on the 

 gland cells of the mamma during secretion; (2), by salts 

 of calcium (phosphates and carbonates) in the process 

 which is termed calcification. We meet the latter very 

 frequently in the cells of many cartilages. Inhaled 

 molecules of charcoal may also accelerate the decay 

 of the epithelial cells of the lungs. 



It belongs to the province of pathological histo- 

 logy to show that the same modes of decay are largely 

 met with in the pathological processes of the system, 

 namely, those of mucous and colloid metamorphosis, of fatty and cal- 

 careous degeneration; likewise that forms of degeneration appear in 

 diseased states of the tissues which do not exist in the normal ; as, for 

 instance, the amyloid ( 21), and the peculiar withering of cells in tuber- 

 culisation. 



Fig. 95. Modes of de- 

 generation of animal 

 cells, a, cells of the 

 Graafian follicle filled 

 with fat; 6, epithelial 

 elements of pulmonary 

 alveoli, replete with 

 pigment. 



B. The Origin of the Remaining Elements of Tissue. 



59. 



Now, it is from these cells of which we have been speaking, and the 

 substance to be found between them, that the remaining elementary parts 

 of the animal body take their rise. 



But, first of all, let it be borne in mind that it is by no means possible 

 everywhere to define sharply between cells and many other elementary 

 parts. Though we have seen, in the preceding pages, that 

 a large number of the various cells preserve their cell- 

 nature unchanged, or with but slight modifications, from the 

 commencement to the end of their existence, still we have 

 also become acquainted with some very striking transfor- 

 mations in their bodies, owing to which they may assume 

 the most anomalous forms. To these may be reckoned 

 the fibre-cells which make up the unstriped muscle of the 

 human body and of all vertebrates. H,ere the cell has be- 

 come a fusiform fibre owing to its nnsymmetrical growth, 

 and the nucleus also, though to a minor extent, has taken 

 part in the process of elongation. While in this example 

 of increase in the length of the cell the nucleus has also 

 become elongated, still, in other similar enlargements, it 

 may preserve its originally oval shape. This is the case 

 in those long transparent cylinders consisting of globuline, which form the 

 fibres of the crystalline lens. 



On the other hand, in some structures multiplication of the nucleus may 

 accompany excessive elongation of animal cells to form tissue elements. 

 This may be observed in a very abundant tissue of the body, namely, 

 in striped muscle. 



The elements of the latter are long cylindrical fibres (fig. 97, 1), of vary- 

 ing thickness, which possess certain contents (2, a) enclosed within a 



Fiir. 96. Contrac- 

 tile fibre-cells. 



