6 DR. G. THIN. 



per-cent. solution of common salt and allowed to remain in it 

 only a few second*. They are then cither at once placed in 

 a drop of glycerine on a glass slip, or are put for a few 

 seconds in distilled water, and thence transferred to the gly- 

 cerine. The glass slip is placed in sun-light. After a 

 quarter to half an hour it will be seen that the free surface 

 of the cartilage is covered with uncolored, generally rectan- 

 o-iilar, spaces, arranged not unlike the stones that form the 

 pavement of a causeway, and between the spaces are fine 

 lines of a darkly stained substance. The white spaces cor- 

 respond, as will be seen, to cells. It is further seen that the 

 cells are arranged in quadrangular, triangular, or irregular 

 groups, and that the groups are separated from each other 

 by broader lines of dark substance than those which sepa- 

 rate the individual cells. 



In the best preparations the widest lines of dark substance 

 do not equal in breadth the diameter of a human red blood- 

 corpuscle, whilst the finer lines between the individual cells 

 are only from one half to a fourth of that breadth. A careful 

 examination will show, in some of the cells, a large round 

 nucleus indicated by a fine unstained ring, which refracts 

 light differently from the substance by which it is 

 surrounded. 



A change of focus brings into view the ordinary ground- 

 substance of the cartilage, stained of a brown colour, and 

 distributed in it the ordinary cartilage-cells, more darkly 

 stained, and irregular in outline. A comparison of these 

 with the nucleated quadrangular cells on the surface shows 

 that they differ in size, form, arrangement, and staining 

 capacity. 



The surface-cells are seen in Fig. 1. The intercellular 

 substance is exaggerated in the drawing. In the best pre- 

 parations the epithelial nature of these cells is evident 

 enough, even if it had not been demonstrated by the potash 

 solution. 



The knowledge obtained by the use of the potash solution, 

 that layers of cells epithelial in arrangement exist in the 

 substance of cartilage, and the now-established fact that silver 

 solution can demonstrate epithelial layers in the substance of 

 the cornea, although the cornea had been treated for years 

 by silver without these having been seen, rendered it reason- 

 able to persevere in an attempt to obtain similar silver pre- 

 parations in cartilage, in spite of a long-continued series of 

 negative results. 



Thin sections made wi;th a very sharp razor transversely 

 through the cartilage co"sWing the condyle of the femur of 



