86 



MANUAL OF HISTOLOGY. 



Fig. 80. Rudiments of a hair from a human 

 embryo sixteen weeks old. a 6, cuticular 

 layers ; m m, cells of the rudimentary hair ; 

 6, transparent layer enveloping the latter. 



In fact, close observation teaches here also that the structures in ques- 

 tion are merely modified, limiting layers 

 of the fibrous tissue of the cutis. And 

 although, in most glandular organs this 

 may arrive at such a degree of indepen- 

 dence as allows of its isolation, still there 

 are other glands destitute of such a mem- 

 brana propria, and in which the groups 

 of cells are simply embedded in a pit in 

 the mucous tissue, bounded by homo- 

 geneous transparent connective sub- 

 stance. 



The consideration of these points in- 

 troduces us to a doctrine in histology originating with Schwann, which 

 for a long time exercised great influence over the progress of development 

 of the science, arid regulated the views regarding the formation of cells. 

 We refer to his theories respecting "cytoblas- 

 tema," or the " ground-substance " of tissues, 

 which, when occurring between cellular ele- 

 ments is known as "intercellular substance." 



If we direct our attention to portions of the 

 body consisting mainly of cells, we frequently 

 find the latter so closely crowded together that 

 they come into immediate contact one with the 

 other, so that at first nothing is to be seen of the 

 matter lying between them which holds them 

 together, and to which the name of tissue-cement 

 This is the case, for instance, in some of the epithelia, 

 such as the flattened species, which line the in- 

 ternal surfaces of serous cavities and blood-vessels 

 (fig. 81). 



Again, layers of cells are to be found in which 

 a connecting medium is apparent between the 

 several elements of the tissue, though perhaps only 

 in small quantity, as, for instance, in columnar 

 epithelium already mentioned (fig. 82). 



When the cells of a simple tissue become more widely separated on the 

 other hand, the intercellular substance in- 

 creases more and more in amount, and com- 

 mences to determine the consistence of the 

 whole tissue. Cartilage supplies us with per- 

 haps the best example of this (fig. 83). 



This intercellular substance is of many 

 kinds, both as to appearance and composition. 

 Thus we meet with it, for instance, perfectly 

 transparent its most usual form without 

 granules, &c., as between the cells of epithe- 

 lium. In many species of cartilage it is milky 

 white; in others finely streaked to a greater 

 or less extent. 



Another kind of cartilage, known as the " elastic " or " yellow." presents 

 a most peculiar appearance : in it the intercellular matter is made up of a 

 tangle of irregularly interlacing bands and fibres (fig. 84). 



Fig. 81. Simple flattened epithe- 

 lium: a, from a serous mem- 

 brane; 6, from the lining of 

 blood-vessels. 



may be given. 



Fig. 82. Columnar cells with 

 intercellular substance, 6 b. 



83. Cartilage cells of various 

 forms with homogeneous intercel- 

 lular substance (diagrammatic). 



