TISSUES OF THE BODY. 



353 



molecules, as well as naked nuclei, and even broken down cells, so that 

 the destruction of numerous cellular masses cannot well be denied. Such 

 cellular debris has long been known ; at an earlier epoch, however, by 

 reversing the order of things, a view of its nature was taken which 

 favoured the theory of the spontaneous origin of cells. 



Another, and it appears equally widely-spread destructive process, is met 

 with in the metamorphosis by which mucin is formed. Ordinary albumi- 

 nous cells made up of the usual protoplasm occupy the parietal portion of 

 the glandular sac, while larger elements containing mucus, and which have 

 had their rise in the first form, are situated in the more central part. By 

 the solution of the latter the mucus of the gland is produced. This is 

 found to take place, for instance, in numerous small mucous glands, such 

 as the labial of man and the rabbit, those of the larynx of the latter 

 animal and the dog, in the submaxillaris of many mammalia, beginning 

 with the dog and cat, and finally, in the sublingual of the dog. 



We shall have to consider these points at greater length among other 

 things in the third part of our work, in referring to the salivary glands. 



The reverse of all this takes place in other glandular organs, as, for 

 instance, in the kidney, where the cells allow the secreted matters to pass 

 through their membrane, repeating again what occurs among the epithelia. 



The question as to how gland cells are regenerated calls for renewed 

 investigation. There can be but little doubt, however, that a process of 

 segmentation takes place 

 among them, for in many 

 organs the occurrence of 

 cells with two nuclei is 

 of great frequency (fig. 

 336, c ; and 337, 6). 



197. 



The vascularisaticm of 

 glands in keeping with 

 their extreme vegetative 

 energy is very perfect. 

 The form of the vascular 

 networks is liable, how- 

 ever, to great variation, 

 being determined by the 

 shape of the glandular 

 elements. Thus race- 

 mose glands are found 

 to possess around their 

 spheroidal vesicles cor- 

 responding bag- shaped 

 capillary networks (fig. 

 342), like those of fat 

 lobules. On the other hand, tubular or follicular glands are supplied 

 with a system of capillaries arranged in more elongated meshes or loops 

 along their walls (fig. 327 and 343), not dissimilar at times to the mode 

 of arrangement of the minute vessels in striated muscle. Around the 

 outlets alone when crowded together do the meshes again assume a cir- 

 cular form (fig. 343 above, and 344 c). The vascular network of the 



Fig. 342. Capillary network from a racemose gland (the 

 pancreas). 



