8 DR. G. THIN. 



the author has only found them on the surface of sections cut 

 fresh, and then submitted to the action of the silver. 



By depressing the focus the uniformly brown ground- 

 substance, with the more darkly coloured cells interspersed, 

 ■was in such sections invariably brought into view. 



There is a certain similarity in the figure to the drawings 

 which have been published by Bubnoif and Hcitzmann. 

 Although in strict detail it corresjionds with neither, the 

 author considers such preparations as confirmatory of the 

 general principle laid down by these histologists, that there 

 are no closed capsules in cartilage. Heitzmann interprets 

 his preparations as demonstrating that the cartilage-cells com- 

 municate by elongated protoplasinic processes. Without at 

 present entering on the question of the existence of such 

 processes, it may be stated that in the author's opinion 

 Heitzmann's drawings show that what he had under his 

 observation was a system of communicating spaces formed 

 by the apposition of two layers being at certain points 

 incomplete. 



Another efiect of the impregnation of the ground-substance 

 is that shown in Fig. 12. 



Such preparations are obtained by removing to an object- 

 glass slip any flat cartilage which is sufficiently thin to be 

 examined entire. 



A piece of solid nitrate of silver moistened with distilled 

 water is rubbed efficiently over both surfaces. The cartilage 

 is exposed to the light in glycerine, and Avhen it has become 

 quite dark is freed from the perichondrium under a dissect- 

 ing lens. (In the frog several distinct layers of large flat 

 polygonal cells, joined like any ordinary epithelium, are 

 found in the perichondrium, and on its surface a thick net- 

 work of lymphatic capillaries is indicated by a black silver 

 deposit.) When sufficiently freed from its investing mem- 

 brane the dark ground- work is seen intersected by a network 

 of white lines which branch from a system of wider and 

 nearly straight spaces, such as that represented in the figure. 

 Either of the sternal cartilages or the thin cartilages which 

 form the walls of the larynx of the frog are well suited for 

 treatment by this method. By changing the focus it is 

 seen that the white lines are present at all depths of the 

 cartilage. 



The third effect of impregnation of the ground-substance 

 which 1 have to describe is of a different kind. It is repre- 

 sented in Fig. 14. The condyle of the femur of a kitten a day 

 old was firmly and persistently rubbed over by solid nitrate of 

 silver, which Avas several times moistened during the operj\- 



