CHANGES DURING PREGNANCY 529 



the maternal organism ceases, and with it the increased protein 

 katabolisni. 



At present this suggestion must be looked upon as an interesting 

 speculation. It still remains to be shown that the introduction of 

 weak proteolytic ferments produces an increased protein katabolism. 

 It is also obvious that gastro-intestinal disturbances must necessarily 

 interfere with the intake and the absorption of food, and may in 

 themselves be an adequate explanation of the diminished nitrogen 

 retention. There is, moreover, one criticism which applies to all the 

 metabolism experiments on pregnant dogs, with the exception of 

 those of Bar and Daunay. At the time when these observations 

 were inade the existence of specific accessory food factors in nutrition — 

 the so-called vitamins — was not known. 



One of the vitamins — tlie " water-soluble vitamin B " — lias a 

 special relation to nutrition. If it is completely absent from the food 

 the animal loses in weight and eventually dies in a state of complete 

 emaciation. It has been shown recently ^ that this is due to an atrophy 

 of the lymphoid tissue wliich normally plays an important part in 

 the absorption or assimilation of food. There is also an impairment 

 in the functional activity of the intestinal epithelium and of the 

 digestive glands leading to interference with the absorption of food. 

 If only very small amounts of this vitamin are present the animal 

 remains in good health, but an abundant supply of it has a distmctly 

 favourable effect on the nutritive condition. In terms of metabolism 

 experiments: the retention of nitrogen is dependent partly on the 

 amount of the water-soluble vitamin present in the diet, in the sense 

 that an abundant supply of this vitamin favours it. The desire to keep 

 the composition of the food constant in metabolism experiments has led 

 unintentionally to the choice of diets poor in vitamins. Thus in almost 

 all the experiments the diet consisted of lean meat, which is poor in the 

 water-soluble vitamin, either alone or with lard, which also is poor in 

 this vitamin, and cane sugar which does not contain any. Bar's diet, 

 in which bread was given with meat, was the only one which from 

 the point of view of vitamin-content was adequate, although by no 

 means ideal. And Bar's dogs showed the best nitrogen retention, 

 although the amount of protein given was much less than in the 

 experiments of those workers who had obtained a negative N balance. 



In order to settle this important point of the importance of 



vitamins in pregnancy, experiments have been carried out in rats.^ 



These were kept on a natural diet of bread, rice, and maize, which, 



though not rich in vitamins, is adequate to maintain the animals in good 



• 



' Cramer, Drew, and Mottram, " The Function of the Lymphocyte and of 

 Lymphoid Tissue, in relation to Nutrition," The Lancet, 1921. "Intestinal 

 Absor'ption, Vitamins, and Eadium," BriL Jour. Exp. Pathol.y 1922, vol. iii. 



2 Cramer (W.), LTnpublished observations. 



