442 A TEXTBOOK OF PHYSIOLOGY 



4. That the fatty substance is derived from the lecithin of the cell. 



5. That the fatty substance is a compound of cholesterin- 

 cholesteryl oleate, possibly derived from lecithin. 



It is quite possible that there are various chemical bodies which 

 give rise to the microscopical appearance known as fatty degenera- 

 tion. It seems very likely, also, that " fatty degeneration " varies 

 in nature according to the tissue in which it is taking place. 



Obesity is usually the outcome of excessive feeding and lack of 

 muscular exercise, particularly the latter. But this is not the only 

 cause, for some people never become fat, however much they eat or 

 however little exercise they take ; others, while eating little and taking 

 much exercise, show a tendency to fatness. The obesity of some may 

 be associated with a greater absorption of foodstuffs from the ali- 

 mentary tract rather than a greater intake of food; that of others 

 is associated with an inadequate oxidation of the foodstuffs, a peculi- 

 arity of their metabolism due, perhaps, to a deficiency of oxidases. 

 An hereditary tendency to fatness is often seen in families. It is 

 well known that different breeds of cattle vary in the readiness with 

 which they can be fattened. The amount of the internal secretions 

 of the sexual glands, and possibly also of the thyroid, may play some 

 part in this tendency to fatness. Castrated animals and eunuchs 

 become fat. This may only be due to laziness developed as a result 

 of the loss of their sexual instincts, but is probably also due to the 

 removal of some direct effect upon metabolism. At the menopause, 

 many women tend to put on flesh. 



We know that the secretion of the thyroid promotes the metabolism 

 of protein and fat, so that a deficiency of thyroid secretion may be 

 a cause of obesity. Thyroid extract is frequently given with success 

 in obesity, but its effects have to be carefully watched. For most 

 cases, a restricted diet, mainly of protein, which of all the foodstuffs 

 most promotes metabolism, and much exercise, is the best treatment. 

 Fresh fruit and green vegetables are bulky, and satisfy the desire 

 for a full stomach. They contain some 90 per cent, of water. The 

 obese should eat these and avoid concentrated foods, such as sugar, 

 fat, meat cooked with fat. 



The truly obese man is an unfortunate. Owing to the large 

 amount of fat, he has much weight to carry, he cannot easily lose 

 heat, his breathing movements are impaired, so that he readily becomes 

 fatigued, quickly gets out of breath, and sweats profusely. The dura- 

 tion of life in the obese is shortened. By giving a few minutes daily 

 to physical exercise of all parts of the body, with bathing, massage, 

 and skin friction, by active exercise on holiday, and a wisely restricted 

 diet at all times, the body can be kept fit and the protuberant belly 

 of the middle-aged citizen avoided. 



