21(3 HEALTH AND DISEASE 



being converted by oxidation into certain animal alkaloids and extractive 

 matters, which exercise a deleterious influence on the organs and functions 

 of the body. Next in importance to the influence of excess or deficiency of 

 food, bad quality may be considered, the immediate effect of which will 

 depend upon the particular constituents which occasion the deterioration. 

 Products of fermentation, growth of fungi (moulds), decomposition, which 

 implies the presence of septic microbes, may render food of bad quality 

 actively poisonous or positively pathogenic, and in such cases it would 

 come under the head of an exciting cause of disease; but short of being 

 actively poisonous or disease-producing, the changes induced in it may 

 merely have the effect of weakening the system without actually producing 

 obvious disease. 



All that has been said in reference to the effects of food may be applied 

 to water, which, indeed, may be taken as representing a portion of the food. 

 Impure air exerts a remarkable influence upon the health of the 

 body in two directions: (l) by failing to supply the proper amount of 

 oxygen for the purpose of respiration and the purification of the circulating 

 fluid; and (2) by introducing into the system organic and inorganic sub- 

 stances which may gradually assist in disturbing the nutritive functions 

 and lowering the vitality of the body as a whole. 



Exertion. — Exercise is a recognized necessity for the maintenance of 

 all the functions of the body, including the mental functions, which are not 

 of first importance with regard to the lower animals. As in the case of 

 food, exercise may be beneficial or injurious according to its amount. 

 Excessive exertion is perfectly well known to be followed by exhaustion, 

 which is necessarily associated with loss of tone in the system and liability 

 to disease. Failure of circulation in various parts will induce congestion 

 and the accumulation of deleterious matters in the blood, and in this 

 condition the body becomes remarkably subject to disease. On the other 

 hand, want of exercise leads to a sluggish condition of all the functions, 

 loss of muscular power, weakness of the heart in common with other 

 muscular structures, feeble circulation, local congestions, inactivity of the 

 respiratory functions, accumulations of fat, and what is perhaps of even 

 more importance, an inactive state of the excretive organs which permits the 

 accumulation in the blood of various deleterious products resulting from 

 imperfect oxidation, which under a healthy condition would be rapidly 

 eliminated from the system. 



Temperature has a marked influence on the various functions of the 

 body; heat causes debility by its stimulating influence upon the circulatory, 

 respiratory, and nervous functions, the excessive activity being naturally 

 followed by relaxation and exhaustion. 



