438 BIOLOGY: GENERAL AND MEDICAL 



It is, therefore, found in the costal and other cartilages, 

 in the blood-vessel walls, and sometimes in other tissues. 



As the calcareous changes come on, the dentine of the 

 teeth becomes] denser and the color of the teeth loses in 

 whiteness and gradually increases in yellowness. 



The digestive organs being altered, the digestive func- 

 tions are inadequate or defective. The eliminative 

 organs are not only themselves defective in structure, 

 but are embarrassed with the imperfectly transformed 

 metabolic products by which further changes in their 

 substance are induced. The general oxidation processes 

 are disturbed; it is difficult to maintain the tempera- 

 ture, and fatigue and exhaustion supervene upon slight 

 effort. In some cases a tendency to obesity presents 

 itself. 



The psychic conditions are adequately explained by 

 the destruction of the nervous tissue through arterio- 

 sclerotic atrophy and softening and by the phagocytic 

 destruction of the nerve cells. It is more difficult to 

 explain the peculiar character of the decadent men- 

 tality, for those familiar with old people well know how 

 acute the aroused mind may be in contrast with its 

 usual apathy, and must have observed how much more 

 vivid are early impressions than recent ones. 



It naturally follows that such enfeeblement of the 

 vital powers gradually causes life to hang upon a very 

 slender thread, so that infections that might easily 

 have been overcome in the vigor of youth are quickly 

 fatal pneumonia being one of the most common causes 

 of death among the aged. A severe mental or physical 

 shock disturbs the delicate equilibrium and the weakened 

 heart may stop. Indeed, in cases in which the process of 

 decadence has been slow, and the anatomical and physio- 

 logical disturbances fairly uniform, no other cause for 

 death can be assigned than the gradual exhaustion of 

 the vital powers. 



In complexly organized beings it becomes necessary 

 to distinguish between somatic and molecular death. 



