HISTOLOGICAL DEMONSTRATIONS. 81 



cartilage cells will be found, and a clear capsule will be 

 seen around most of the protoplasts thickest in the largest 

 ones. The appearance reminds one of the capsule enclosing 

 each protoplast in white fibro-cartilage. The diffuse picric 

 acid staining is of much service in rendering these capsules 

 evident. The matrix of hyaline cartilage apparently consists 

 of these capsules pushed outwards and matted together by 

 new ones that are secreted by the protoplasts proliferating 

 by fission within the old ones. Side by side with the 

 proliferation of the cartilage cells, observe the fibrillation of 

 the matrix. This consists in the appearance of great 

 numbers of calcified fibrils running parallel one with 

 another, and usually with the long axis of the groups of 

 proliferating cells. The proliferation of the cells and the 

 calcified fibrillation of the matrix are the two earliest stages 

 of intra-cartilaginous ossification, which will be further 

 studied in another preparation ( 125). If this preparation 

 happen to be the costal cartilage of an old subject, cartilage 

 cells in a state of fatty degeneration may be found here 

 and there. The protoplasm becomes replaced by fatty 

 particles. 



117. Staining Agents for Hyaline Cartilage. a. Osmic 

 acid. The fatty particles that occur sparingly in most cartilage cells, 

 and often so abundantly in those of an old subject, may be readily 

 demonstrated by placing the slices in \ per cent osmic acid for 12 to 

 24 hours. The fat is blackened by the acid. 



b. Chloride of gold is very useful for staining the cells. It renders 

 them violet, and it has the great advantage of not causing any retrac- 

 tion of the protoplasm from the matrix. Vertical or longitudinal sec- 

 tions of the articular cartilage of the femur of a frog, recently killed, 

 when stained with gold give readily the characteristic appearance. It 

 should be kept in the gold solution twenty minutes, and otherwise 

 treated as described in 330. 



c. Silver Nitrate stains the matrix of hyaline cartilage, and is there- 

 fore of value in tracing its relation to the protoplasts. Ranvier's 

 method is to wash the head of the frog's femur in distilled water for a 

 few seconds ; place it in \ per cent solution of silver nitrate until it 

 becomes opaque ; wash in distilled water for some minutes : remove 

 thin slices from the articular surface ; place them in glycerine on a 

 slide, and expose to the light till the matrix has become sufficiently 

 dark. Or the articular surface may be shaved off, and the sections 

 placed at once in the silver solution. 



d. The value of picric acid has been alluded to in 1 16. 



G 



