TISSUES OF THE BODY. 233 



puscles, supposed to be supplied with, membranes, constituted a hollow 

 system of canals, like that to be met with in bone, for the con- 

 ducting of certain definite nutritive fluids through the tissue, forming 

 thus a,plasm,atic circulation. Eased on this view, the name of sap canali- 

 culi was given by Koelliker to these passages. But there was no phy- 

 siological necessity for supposing that this must be the case in connective- 

 tissue, in that it does not occur in cartilage. Besides, the system of 

 interstices in parts formed of connective-tissue would appear but little 

 suited for the fulfilment of such an object, frequently stopped as they 

 are by cells, and compressed by the intermediate substance. Communica- 

 tions between these interspaces and the vascular systems do not occur, 

 either with the blood-vessels or lymphatics, although this erroneous doc- 

 trine still permeates histology. 



The question now arises, which of the elements of form are to be 

 looked upon as physiologically the most active and important in con- 

 nective-tissue masses 1 Here also as anatomically the decision must be in 

 favour of the cells, so long as the latter possess even a small remnant 

 of their body. On the other hand, connective-tissue structures, in which 

 the cellular elements no longer exist, and where alone dense networks of 

 elastic fibres remain, must be looked upon as tissues endowed with a 

 minimum amount of life ; for instance, the ligamentum nuchae. 



Among the transformations of senescent connective-tissue we must now 

 bestow a few words on calcification, occurring in a similar manner to that in 

 cartilage, and by no means rarely. Bony tissue may likewise take the 

 place of the former, but much more seldom by direct transition of one 

 tissue into the other as by a neoplastic process, corresponding to that 

 which takes place in the embryo, where the newly-produced bony mass 

 takes up the place of the vanishing connective- tissue. We shall be 

 obliged to refer again to this question in considering osseous tissue. 



We are now met by another difficult question, namely, how far con- 

 nective-tissue cells may become transformed into the elements of other 

 tissues not belonging to this group. It appears plain that, with their 

 power of vital contractility, no great distinction can be made between 

 them and the cellular elements of unstriped muscle. And yet there 

 have been long and indeterminable controversies as to what are muscle 

 and what connective-tissue cells in certain organs, e.g., the lymph glands 

 and the ovary. We have already stated ( 98) that the so-called endo- 

 thelia must take rise from the cellular elements of connective-tissue. On 

 the other hand, there appears to be no transition into the cells and 

 offspring of the corneous and intestinal glandular plates, and there seems 

 further (if we except the neuroglia and many portions of the higher 

 organs of sense) to be no true connection between these tissues. It 

 is true that such intercommunication has been frequently asserted to 

 take place, as, for instance, in the intestinal villi by Heidenhain. Here 

 long processes of the cylinder-epithelial cells are stated to be united 

 with those of the connective-tissue corpuscles of the sustentacular sub- 

 stance of the villus. These statements have not, however, been corrobo- 

 rated. 



The contractile and wandering lymphoid cells of connective-tissue have 

 been already dealt with in a former section. That they generally take 

 their rise from the derivatives of the middle germinal plate in enormous 

 numbers there can be no doubt. 



It is a striking fact, ascertained by Virclww, that connective-tissue, 



