100 LOCOMOTION. [CHAP.V 



consists in a deficient deposit of earthy matter ; the animal matter 

 being probably of an unhealthy quality. In this disease the bones 

 are so flexible, that they bend under the weight that they may be 

 called on to support, or under the action of the muscles. The 

 lower extremities exhibit deformity first, and to the greatest degree, 

 ? nd the direction in which they become bent is evidently influenced 

 by J\e superimposed weight ; the bend almost always appears as 

 an aggravation of the natural curves of the bones. The rickety 

 femur has always its convexity directed forwards : the tibia is con- 

 vex forwards and outwards, and the fibula follows the same direc- 

 tion. When the nutritive powers of the system are fully restored, 

 the deposition of earth goes on in its healthy proportion, the animal 

 matter becomes healthy, and the bones acquire their due degree of 

 strength and hardness. In the tibia of a rickety child, Dr. Davy 

 found, in 100 parts, 74 parts animal matter, and 26 earthy; and 

 Dr. Bostock found in the vertebra of a similar subject 79' 75 animal, 

 and 20-25 earthy. 



The brittleness of the bones in old age is due to an opposite cause, 

 namely, the defective deposit of animal matter, so as to give to the 

 earthy matter the undue preponderance already specified. But this 

 state cannot be looked upon as morbid; it is the natural result of 

 the feeble condition of the powers of nutrition, which ensues in the 

 advance of years ; and it will vary, in different individuals, accord- 

 ing to the original strength of constitution of each, and according 

 to the freedom from exposure to debilitating influences. 



That state of bone which accompanies malignant disease (cancer, 

 or fungoid disease) in adults or old persons, and which some patho- 

 logists have designated mollities ossium, results from the dissemi- 

 nation of cancerous matter through the system. In this disease, the 

 whole nutritive process of bones seems tainted; the animal part is 

 not so much deficient in quantity as bad in quality ; the physical 

 as well as the vital properties of the bone are completely deranged; 

 the osseous texture has lost its cohesive power. Hence these bones 

 often break on the application of the slightest force, or on the 

 feeblest exercise of the muscles. They are soft, too, in the recent 

 state ; the knife will sometimes penetrate them ; and they are often 

 pervaded by a considerable quantity of oil. 



Bones possess a remarkable power of resisting decomposition. 

 Even the animal part seems to acquire this power through its coi 

 bination with the earthy. This is manifest from analysing bon< 

 which have been long kept, or fossil bones. Cuvier states thj 

 the latter bones exhibit a considerable cartilaginous portion ; an< 



