TISSUES OF THE BODY. 193 



appear elastic fibres (at least in animals). The network also shows 

 increase of the distance between individual cells, a development of long 

 filiform processes, and the bodies of the former, in which, however, a 

 nucleus is still apparent, become smaller as the processes are extended 

 (c, d, e). 



For the rest this cellular network displays at a later period much 

 variety ( Weismanri). In its power of resistance towards reagents it re- 

 minds us of elastic matter, whilst, on the other hand, it is rapidly acted on 

 by alkalies in contradistinction to the latter. 



"We have before us here, then, a connective-tissue transformation which 

 is far advanced when at birth the death of the tissue takes place. 



The soft, structureless connective-tissue of early life has just the same 

 nature. In its meshes likewise, as Schwann has shown, the same rounded 

 cells are to be found, which possibly become fat-cells eventually. The 

 banded portions of both these tissues yield originally no glutin on being 

 boiled. 



REMARKS. The origin of the enamel organ appears indeed to be peculiar, in that 

 it takes place from epithelium (comp. chapter on the teeth). Of the truth of this 

 statement we are assured by KoUiJcer, after due examination of the development of 

 the teeth. Further investigation of the matter is desirable, however, considering 

 the great histological interest which attaches to the subject, and the difficulty of such 

 embryological research. 



117. 



Having now concluded the consideration of gelatinous tissue, we turn 

 to another member of the so very varied group of connective-substances, 

 namely, to the reticular the adenoid of His, or cytogenic of Kolliker. 



Here we encounter similar networks of radiated connective-tissue cells 

 (subject, however, in individual cases to much variation), which are meta- 

 morphosed into fibres or fasciculi of more or less extensive course, and 

 may receive also coatings of a streaky or fibrillated intermediate substance. 

 The spaces, however, incompletely enclosed by them, are not filled with 

 mucoid jelly, but by structural elements, by innumerable lymphoid cells, 

 such as are found in lymph, chyle, &c. 



A considerable number of organs possess a tissue of this kind. For 

 instance, the framework of the lymphatic glands is composed of it, as well 

 as that of those lymphoid organs so nearly related to the latter, namely, 

 the tonsils, thymus gland, and follicles which are met with, isolated or in 

 groups, imbedded in the intestinal tube and conjunctiva. The Malpighian 

 corpuscles also of the spleen consist of reticular connective-substance. 

 The latter again, although presenting many varieties, forms, among the 

 higher animals, the mucous membrane of the small, and partly of the 

 large intestine ; and, finally, it is met with, strongly modified, in the 

 pulp of the spleen. 



Here also we encounter again certain peculiarities, already frequently 

 mentioned. In the first place, we see in such organs the peripheral por- 

 tions undergoing further changes in their reticular connective-substance, 

 through which the latter may eventually become converted into ordinary 

 fibrous tissue. Further (and this is the case, for instance, in the intestines 

 of the lower animals), the reticular substance may be replaced by the latter. 

 Finally, it may spring from ordinary connective-tissue under pathological 

 conditions, on the other hand, or become transformed into the latter. 



As elements we meet with stellate cells (fig. 184), whose nuclei have 

 smooth borders and a nucleolus, and measure, on an average, 



