RICKETS. 199 



Emily. What is the chemical composition of the 

 bones ? I should imagine that strong materials were re- 

 quired. 



Dr. B. The bones are formed of two kinds of sub- 

 stance, one animal, the other earthy. The latter serve 

 the purpose of giving the necessary firmness and solidity 

 to the bone ; but this alone being exceedingly brittle, a 

 certain portion of animal matter is obviously required, 

 to give it flexibility and power of resistance. 



Emily. Fray how do you know so exactly what are 

 the particular uses of these two different substances. I 

 should like to see some little more satisfactory evidence 

 of it, than the mere assertion of the iact. 



Dr. B. -You have noticed no doubt, how brittle, bones 

 are, that have been burnt in the fire, now if these be 

 analysed, they will be found to have lost all their animal 

 matter. On the other hand, here is a bone which has 

 been kept some time, in a jar of diluted muriatic acid, 

 and you see that though quite a stout bone, I can easily 

 bend it up double without breaking it. 



Emily. Well, that is singular indeed ! But you must 

 have the kindness to explain it. 



Dr. B. The acid has united chemically with the 

 earthy portions of the bones and removed them, leaving 

 behind only the animal matter, which being very flexi- 

 ble yields to the least force. Do you see now, that 

 bones formed of either of these substances alone would 

 want either firmness or flexibility ; but that being com- 

 posed of both, they possess a proper share of both, these 

 qualities ? 



Emily. Yes 4 see perfectly well now, how both 

 strength and flexibility are obtained by the union of these 

 different kinds of substance. 



Dr. B. You have seen children perhaps, effected 

 with the disease called rickets, when the limbs sink un- 

 der the weight of the body. Here, owing to some de- 

 tect of nutrition, the bones are not supplied with their 

 proper portion of earthy matter. The contrary takes 



