ELEMENTS OF STRUCTURE. 



G9 



Fig. 5-J. 





extracted by alcohol. These membranes exist in many cellular formations 

 of the body beyond question. Their purposes appear 

 chiefly anatomical, in that the consistence requisite for 

 many animal tissues is, as we know by experience, greater 

 than could be yielded by the soft protoplasm of the cell- 

 body alone. 



Where, however, the individual cells are widely 

 separated by considerable quantities of solid intermedi- 

 ate substance, or where just the reverse is the case, 

 and they are suspended in a liquid, forming a fluid- 

 tissue, this membrane is probably absent as a rule, 

 Such cells are those of dentine tissue and of bone, as 

 also the cellular elements of the blood, the lymph, and 

 the liver (fig. 52). 



The membranes of cells are usually transparent, and, as far as we can 

 see with our present optical instruments, structureless and without open- 

 ings or pores. Attention has, however, been lately directed to certain cells 

 in which pores may be distinguished by means of the microscope a cir- 

 cumstance into which we shall have to examine more closely further on. 



It is probable, also, that in isolated cases this cortical layer or envelope 

 covers only certain portions of the body of the cell. 



As a rule, we find the demarcation of a cell such that a smooth contour 

 encloses the figure ; but it may happen that the 

 granular contents produce a rugged appearance on 

 the surface, which leads us involuntarily to the dis- 

 tinction between smooth edged and granulated cells 

 (fig. 53, a d). Both of these differences are, how 

 ever, of minor importance. Again, owing to a par- 

 tial exit of the matter contained within, the cell, 

 which had been up to that time perfectly smooth, 



. *, , , ..r 



may assume a wrinkled appearance ; while, on the 



other hand, the reverse may take place with a 



granulated cell through the imbibition of water ; it may swell out and 



become a smooth rounded object. 



Attention has lately been directed by M. Schultze 

 to a remarkable appearance in the borders of young 

 cells, and especially those of flat epithelium ; their 

 surface, namely, is completely covered with points, 

 ridges, and prickles, as they might be named (fig. 

 54), which fit in among those of the neighbouring 

 cells "like the bristles of two brushes which have 

 been pressed against one another." The appropriate 

 name of " spinous and furrowed " cells has been 

 given to these. 



5. If we now turn to the analyses of the nucleus, 

 with its adjuncts, we meet with a certain vari- 

 ability in it likewise. First, the difference in size 

 of the various animal cells brings with it very con- 

 siderable fluctuation in the diameter of the nucleus ; 

 proportionately less, of course, than that of the 

 cell itself. We may accept O'OOl 1-0-075 mm. as 

 a medium diameter for the nuclei of animal cells ; 

 but at the same time, it must be borne in mind that some may be found 



t 6 c, Smooth-eaged 

 diskoid blood - corpuscles, 

 with one granulated white 

 cell (d) whose nucleus is ob- 

 scured. 



Fig. 54. Spinous or far- 

 rowed cells, o, from the 

 undermost layers of the 

 human epidermis; b. a 

 cell from a papillary 

 tumour of the human 

 tongue (copied from 

 Schultze.) 



