TISSUES OF THE BODY. 351 



kinds of cellular elements, as, for instance, in the submaxillary and peptic 

 glands of many mammals. "We shall refer to these again. 



Differences in gland cells have also been remarked corresponding to 

 their conditions of activity and rest, e.g., in the glands of the stomach and 

 submaxillary of niaiiy mammals, &c. 



Finally (en passant), between the hepatic elements, and later still 

 between those of several racemose glands, a system of the most delicate 

 canals has been met with, to which the name of " gland capillaries " has 

 been given. Fig. 339 will give some idea of the nature of these. 



Turning now to the size and further composition of the gland cell, we 

 observe great diversity, especially in the former. Those elements, for 

 instance, clothing the internal surface of the ovarian vesicles, possess a 

 diameter of only 0'0074-0'0090 mm., while the roundish polyhedral cells 

 of the racemose mucous glands measure G'0068-0'0113 mm., those of the 

 peptic glands -0226-0*0326 mm., and those of the liver almost as much, 

 &c. In these cells are to be found single, or not unfrequently double, 

 nuclei of from 0'0056 to 0*0090, at one time vesicular, and at another more 

 homogeneous. At a later period, in the more mature cell, these may, how- 

 ever, become dissolved. The contour of such elements is usually very deli- 

 cate, and their contents are of various kinds ; this we shall again refer to. 



196. 



The delicate constitution of the cells in question, together with the 

 lively interchange of matter which is carried on through their agency, 

 tends to render the existence of a certain number of them very transitory, 

 showing again another parallel with many epithelial elements. But while 

 we are able to demonstrate the briefness of the existence of many cells 

 with all the certainty desirable, we have no facts to support us in other 

 cases, nay, we even have observations which point to the very opposite 

 conclusions as regards them. Thus the hepatic (fig. 337) and renal cells 

 are known to be comparatively permanent elements. 



Here again, as among the epithelia, mechanical wear and tear takes 

 place also, the stream of fluid which flows towards the outlet of the 

 gland carrying off with it greater or smaller quantities of the cellular 

 lining. If we observe, for instance, the stratum of mucus which covers 

 the coats of the stomach while digestion is going on, especially among 

 phytophagous animals, we may frequently discover extraordinary numbers 

 of peptic cells swept away in the gastric juice which wells up from below. 

 The sebaceous secretions of the skin contain likewise cellular elements 

 derived from the glands, from whence they emanate. In other organs, 

 however, such as the kidney, lachrymal, and sweat glands, the cells appear 

 to be washed away to a smaller extent, and in the bile hepatic cells are 

 never to be found. 



The transient nature of these elements is manifested again in another 

 way. They are destroyed, namely, to form the secretion of the gland to 

 which they belong. Without taking into account such peculiar changes 

 as lead to the, origin of spermatozoa within the cells of the seminal 

 tubules, we find the most ordinary mode of decay to be in physiological 

 fatty degeneration, as it may be expressed, of the elements of glands. 

 Here the cells are observed to be destroyed by the generation within 

 them of fatty contents, undergoing subsequently a process of solution 

 by which the latter are liberated, and appear as constituents of the 

 glandular secretion. This is found to take place in the sebaceous glands 



