THE SUPPORTING TISSUES. 99 



three bones that form the- os innominatum, unite about the 

 same time. Thus we may see that the human body does 

 not reach its skeletal maturity until about twenty-five years 

 of age. From a hygienic standpoint this ought not to be 

 forgotten, for loads that a man of thirty may carry without 

 the least danger, may prove disastrous for a lad of eighteen 

 or nineteen, in spite of the strength of his muscles. 



Some interesting experiments have been made in order 

 to determine the manner of growth of bones, by feeding 

 young pigs madder. In this madder there seems to be a 

 compound which colors bone in which it is deposited red. 

 When, now, such a pig in question has for a month or two 

 been fed with madder, and is then killed and the bone 

 examined, it is found that there is a layer of reddish bone 

 immediately under the periosteum and zones at the ends 

 where the cartilage has been encroached upon. All the 

 bone, however, next to the medullary cavity remains un- 

 stained. By taking such a pig and feeding it this madder, 

 in alternate months, it is possible to produce characteristic 

 rings of red and white, encircling the shaft of the bone 

 under the periosteum and zones of red and white alternat- 

 ing at the extremities. That the shaft itself does not grow 

 is easily demonstrated by driving some pointed pegs into 

 the shaft of a living bone, and then measuring their relative 

 distances after a certain period has elapsed. In the shaft 

 of the bone these pegs do not separate, showing that no 

 elongation has taken place. If, however, one of the pegs 

 be inserted in the cartilaginous end the regular elongation 

 appears. 



The bone which is deposited under the periosteum is 

 deposited in successive layers, much like the layers of an 

 onion. These layers of lamellae do not show the character- 

 istic arrangement of the Haversian systems, as described 

 on a former page. To explain how these circumferential 

 lamellae become later changed into the characteristic Haver- 

 sian systems is at present no easy matter, but it is believed 

 on good grounds that the circumferential lamellae are actu- 



