212 



MANUAL OF HISTOLOGY. 



elasticity of the membrane. Thus we remark at first the fragment of the 

 sheath still long and transversely ribbed (3 /;), but soon, and especially when 

 from both ends of the torn sheath the contents swelling out press upon the 

 latter, that portion of the envelope contracts into a fine narrow ring with a 

 dark contour (2 a, 3 a) ; more rarely, in consequence of 

 a spiral rent, it shrinks into a filiform structure passing 

 round the mass with a spiral course. Did we not know 

 their origin, we might look on these shrunken fragments 

 of the envelope as fibres of a coarser kind, encircling 

 either as rings or spirals the bundle of connective- 

 tissue. It is an interesting fact that fibres of cotton 

 undergo the same changes, under the action of am- 

 monio-oxide of copper, which may here be observed 

 in all their phases with the most perfect ease. 



It seems, therefore, beyond doubt that elastic mem- 

 branes may shrink into filiform structures in conse- 

 quence of being completely rent. 



We are here met by the question, whether something 

 similar to this, which we have found as an artificial 

 production, may not also occur as a normal process in 

 many of the elastic membranes of the body, whether, 

 by a partial reabsorption or rending of its substance, 

 a membrane of this kind may not be converted into a 

 network of elastic bands and fibres, at the same time 

 that its substance so fenestrated diminishes greatly in 

 extent owing to elasticity. 



There seems, indeed, to be no doubt that networks 

 of elastic fibres or flat bands, as we meet with them in 

 the middle coat of the greater arteries in large mammals (fig. 206), have 

 frequently had their origin in the manner just described. It is probable 

 also that, by the thickening of elastic membranes at particular points in 

 folds and bands, a network of elastic tissue may be formed (fig. 203). 



129. 



We turn now to the most difficult point in this subject, to the cellular 

 constituents, or, as they were formerly called, connective-tissue corpuscles. 

 In them we have the most important physiological elements of the tissue 

 under consideration. As we have already remarked, these cells are usually 

 obscured by the fibrillse around them, and only come into view after the 

 use of acetic acid and other strong reagents, amid the gelatinised ground- 

 substance. But where it is possible to obtain a view of the still living 

 and unchanged connective-tissue corpuscle, it is very far removed in 

 appearance from those which have been acted on by reagents. 



Besides the true connective-tissue cells, all the structures we are en- 

 gaged in considering appear to contain a second element, the lymphoid 

 cell, which has migrated from the blood-vessels. The "cells of connective- 

 tissue might, therefore, be classed with propriety into fixed and wan- 

 dering. 



Let us turn now to the living tissue. 



An excellent spot for obtaining living connective-tissue was pointed 

 out not long ago by Kilhm : this is in those thin transparent lamellae 

 which occur between the muscles of the leg of the- frog. 



In one of these (tig. 207), we may see in the extremely soft ground- 



20C. Elastic nets 

 from the aorta. 1. 

 An elastic fenestrated 

 membrane from the 

 ox; 2. A distinct net- 

 work of broad fibres 

 from the whale. 



