CHAP. V.] EXPERIMENTS WITH MADDER. 123 



encircled by a crimson ring. This beautiful illustration is due, as 

 far as we know, to Mr. Tomes, who has long possessed some very 

 elegant specimens prepared in this way. 



In full-grown animals the bones are very slowly tinged, because 

 the great mass of the bone is not in contact with blood-vessels ; each 

 Haversian system, for example, has only its small innermost 

 lamella in contact with them ; and, besides, the osseous matter is 

 altogether more consolidated and less permeable by fluids than at 

 a very early period of life.. In the bones of half-grown animals a 

 part of the bone is nearly in the perfect condition, while a part is 

 new and easily coloured. Hence, it is easy in them to distinguish 

 the new from the old by means of madder. 



Now, madder given to half-grown animals colours the long bones 

 most deeply in the interval between the shaft and extremities, and 

 on the surface of the shaft. When madder is given at intervals, the 

 tints in the bone are interrupted ; the layers in course of forma- 

 tion during its administration are coloured, while those formed 

 during the intervening periods are colourless. The long period 

 during which bones retain the madder tinge, shews that the colour- 

 ing matter is not readily resumed by the blood, from its combina- 

 tion with the phosphate of lime ; and it seems also to indicate a 

 sluggishness of the nutrient process in bone. 



Perhaps few questions have more divided the minds of physiolo- 

 gists than that regarding the share taken by the periosteum in the 

 growth and regeneration of bone; for these last are essentially the 

 same process. We now see that bone does not grow on its exterior 

 because the periosteum is there; and that the only part this mem- 

 brane takes in the deposit of new bone is by the vascular network 

 mingled with its fibrous tissue, and which does not differ from that 

 on other portions of the osseous surface. 



The limited expansibility of the bone already formed is the 

 remote cause to which the growth by new deposit on the exterior is 

 to be referred ; and, in this respect, the superficial growth is strictly 

 analogous to the exogenous mode of growth in vegetable struc- 

 tures. 



A third mode in which increase of size is provided for, appears 

 to be by the dilatation of the primary cancelli and Haversian canals 

 in the central parts of the bone. In early life the cancelli are 

 small, and there is no medullary cavity. Gradually the cancelli 

 enlarge, and those within the shaft blend more and more with one 

 another, by the removal to a greater or less extent of the interven- 

 ing osseous walls, until at length a medullary canal is formed, 



