12 PHYSIOLOGY CHAP. 



one, when the magnitude of the figures for the balance of the 

 intake and output is taken into consideration. 



As regards the non-nitrogenous substances contained in the 

 faeces, it is well to remember that a noteworthy amount of fat can 

 always be extracted from them with ether, even when the food is 

 devoid of fat and even from the faeces formed during fasting. 

 Rubner found that the faeces contained 3'1-6'S grms. of ethereal 

 extract when the diet of an adult consisted solely of bread or 

 macaroni, which contain a very small quantity of fat. It may 

 therefore be assumed that when the quantity of fat contained in 

 the faeces in twenty-four hours does not exceed 6-7 grms., it does 

 not represent a residue of fatty foods, but an excretory product 

 which is to be reckoned with the output. Likewise in Atwater's 

 researches with an ordinary mixed diet the quantity of fat in the 

 faeces varied from 2'1 to 13*4 grms., an average of 5'1 grms. per day. 



There is also found in the faeces a certain quantity of carbo- 

 hydrate, varying with the nature of the food. We know, in fact, that 

 cellulose is not attacked by the digestive juices, but only by a process 

 of fermentation set up by bacteria, and requiring the retention of 

 the food for a long time in the intestines, which is not the case in 

 man. It is therefore obvious that the quantity of carbohydrate 

 in the faeces will be the smaller the less the cellulose introduced 

 with the food. This is confirmed by the observations of Rubner, 

 Hultgren, and Landergren. On a diet of brown rye bread the daily 

 quantity of carbohydrate in the faeces varies from 38 to 72 grms.; 

 on a diet of white bread, macaroni, and rice it does not exceed 

 13-14 grms. 



Without any considerable error it is possible to estimate 

 indirectly the quantity of carbon contained in the faeces by 

 taking as a basis the proportion between the nitrogen and the 

 carbon, which according to Atwater and Benedict's investigations 

 has a mean value of 1 : 9'2. 



III. A clear and instructive example of the total balance of the 

 intake and output of the human body is given by Schenck and 

 Giirber (1900). The subject of the investigation was an adult man, 

 living on meat, bread, butter, potatoes, common salt, and water. His 

 initial weight was 70 kgrms. He remained at rest for twenty- 

 four hours in the chamber of Voit's respiratory apparatus, and at 

 the end of the experiment he had gained 139 grms. in weight. 



The nutritive substances taken were as follows : 



Grms. of Carbon. Grms. of Nitrogen 



Protein ... 130 gnus, containing 69 21 



Fat . . . .100 76 



Carbohydrate . 400 176 



SaU*- ... 30 



Water 2100 



Total intake of food 2760 321 21 



