As ossification advances in the bones and gelatine is consequently carried to them in less quantity, it seems that it goes more abundantly to the articular surfaces; for the cartilages that are met with, then lose their primitive softness, and have a consistence that is constantly increasing. Yet much more gelatine leaves the bones, than is carried to the cartilages; so that we may say that this substance is continually diminishing, in the organs, in proportion as we advance in age. We know that it is the parts of young animals particularly, that are selected to make glue, jelly, &c. The articular cartilages at this period exhibit a phenomenon that I have frequently noticed in my experiments; when we macerate them in water for two or three days, they take a very evident red colour. This colour does not penetrate deeply; but if we cut the cartilage in many places so as to bring the fluid in contact with its interior, the whole of it becomes red. The cartilages of ossification exhibit the same phenomenon, which becomes less conspicuous as we advance in age; so that in adults generally, the cartilages do not lose their white colour by maceration. In some however they take a reddish tinge which is infinitely less bright than in the fœtus. Whence arises this phenomenon? Does the water give to the cartilage the cause of its colour, or does it take from it by solution certain substances which prevented this colour from being developed? Whatever may be the cause, none of the organs of articulation redden in this way; all on the contrary, the synovial, the ligaments, &c. become whiter. There is usually no sensible demarcation between the cartilage that is to become bone, and that which is to remain as it is; sometimes however on the one hand we observe it a more dull colour at the extremity of the bones, whilst on the other, we never discover the reddish streaks, which are so frequently seen irregularly scattered on the cartilages of ossification. As long as ossification continues, there is between the cartilage and the osseous portion already formed, a very evident vascular layer, and it is extremely easy to separate these two portions, which adhere but slightly to each other. We observe also on the surface of each when they are separated, several inequalities, projections and depressions reciprocally adapted to each other. It is the want of adhesion of the cartilaginous and osseous portions, before complete ossification, which has no doubt given rise to all that has been written upon the separation of the epiphyses, a separation which the observations of modern surgeons have rarely confirmed.