168 MANUAL OF HISTOLOGY. 



memoirs on the subject as, for instance, those of Virchow, Donders, and 

 others are no longer serviceable in the present condition of histology. 

 And, finally, owing to the difficulty of investigation, and a certain amount 

 of weariness produced by unprofitable discussions, the connective-tissues 

 have recently been somewhat neglected by microscopists. 



The following are about all the features we can pronounce as histologi- 

 cally characteristic of the group of connective substances : 



The embryonic rudiments of all the tissues in question consist origi- 

 nally of aggregations of more or less spheroidal formative cells, without any 

 membrane, and enclosing vesicular nuclei. Between these a soft, homo- 

 geneous intercellular substance, consisting of albuminous matter, begins 

 to be formed, be it as a product of the cells, or as a transformed portion 

 of the cell-bodies. This appears later on in considerable though varying 

 abundance. Subsequently the cells as well as the intercellular matter 

 commence to take on other forms. As a rule, the ground-substance or 

 matrix undergoes more or less a division into fibrous or stringy masses or 

 a transformation into fibrillae, while the cells become stunted, or on the 

 other hand develop into spindle-shaped or stellate elements, which again 

 may unite to form a cellular net-work. Calcification likewise of the 

 intercellular substance is a typical occurrence in some of the tissues under 

 consideration. 



And with these anatomical changes we find besides corresponding 

 chemical metamorphoses. As we have just said, the ground-work of con- 

 nective-substance consists originally of protein matter or near deriva- 

 tives of the same. A substance nearly allied to, or identical with, 

 mucin (p. 21), also makes its appearance here very frequently. Almost 

 everywhere the chemical constitution of earlier days is missed, more 

 remote descendants of the protein group appearing, namely, the glu- 

 tinous substances (p. 22), and amongst them usually glutin or more rarely 

 chondrin : local transformation of the ground-substance into elastic mate- 

 rial (p. 23) may also take place. In the cell-body also the original proto- 

 plasm may be replaced by other matters, such as pigments, fats, &c. 



Now, as we have already remarked, a classification of the tissues be- 

 longing to this group must be looked upon as a doubtful matter, owing 

 to the intermediate forms and transitions which are constantly en- 

 countered. We will, however, distinguish between 1. cartilaginous; 

 2. gelatinous and reticular connective-substance ; 3. fatty tissues ; \. ordi- 

 nary connective tissue; 5. bony tissue; and, 6. dentine. 



5. Cartilage. 

 103. 



By cartilage we understand a compact tissue (appearing very early in 

 the embryo, often rapidly maturing and as often rapidly decaying), which 

 is widely distributed throughout the body, and formed of cells situated in 

 an originally homogeneous intercellular substance. The specific gravity of 

 cartilage in keeping with its solidity is considerable, amounting, according 

 to W. Krause and Fischer, to 1'095 and 1'097 for that of the joints 

 and the ear. The flexibility and elasticity of cartilage is by no means 

 inconsiderable when in thin pieces or plates; but thicker pieces are brittle, 

 and snap easily. 



According to the regions in which they occur, anatomists have 

 divided cartilages into articular, or such as clothe the extremities of 



