DISCUSSION OF RESULTS AND GENERAL CONCLUSIONS. 95 



special experimental conditions it is possible for us to add to or take from the 

 store of nitrogen in the body to the extent of several hundred grams, never- 

 theless this is rarely accomplished. Consequently, in studying fluctuations of 

 body-weight ordinarily occurring outside of those attendant upon wasting dis- 

 eases, we do not need to consider any alterations in the storage of body nitrogen. 



One of the most important compounds in the human body is the relatively 

 small quantity of carbohydrate material, chiefly in the form of glycogen in the 

 liver and muscles. While it is believed that there may be, relatively speaking, 

 a large draft upon this storage of body-glycogen, which has been estimated by 

 some writers to be not more than 400 grams, the total fluctuation one way or 

 the other is not of sufficient moment to play any part in considering the major 

 changes in body-weight. It is possible, indeed probable, that varying amounts 

 of glycogen may indirectly control or influence the presence of varying amounts 

 of water, but glycogen per se can not be materially added to the body or taken 

 from the body, since the total storage is small probably not far from 400 

 grams. The remaining compound of the body, i. e., fat, can, however, be 

 enormously added to or taken from. It is with changes in the storage or loss 

 of fat that we have chiefly to do when discussing the question of the gains and 

 losses in body-weight, particularly losses that are the result of a progressive 

 change covering some weeks or months. 



It has already been pointed out how by certain abnormal conditions we 

 can produce rapid fluctuations in the water-content of the body, but it is prac- 

 tically impossible to secure any rapid change in the amount of fat stored or lost 

 by the body. Even fasting for a day does not lead to any appreciable draft 

 upon the storage of fat. It has been proved that in a normal healthy indi- 

 vidual undergoing a complete fast for 24 hours, the glycogen may be depleted 

 to the extent of possibly one-half of its original value. Then after this deple- 

 tion of glycogen has taken place, the fat is drawn upon, and after the third day 

 the draft is chiefly upon the fat-content of the body, with a relatively small but 

 constant depletion of the glycogen and protein ; thus it is seen that any changes 

 in weight having to do with 1 or 2 pounds inside of 24 hours can not in any 

 way be considered as changes in the fat-content of the body. 



To studjr the character of these changes, respiration experiments are essen- 

 tial, in which the carbon-dioxide production is determined as well as the oxygen 

 intake and, if possible, the vaporization of water. If we were to collect all of 

 the products of expiration from the body, namely, the carbon dioxide and 

 water-vapor, we would not even then have an equivalent of the material lost 

 from the body, for of the carbon dioxide and that portion of the water which is 

 formed by the oxidation of organic hydrogen, a not inconsiderable amount is 

 due to the weight of the oxygen absorbed from the air. For instance, assuming 

 that a man at rest in 24 hours produces 700 grams of carbon dioxide and gives 

 off 900 grams of water by sensible and insensible perspiration, this total weight 

 of 1,600 grains does not by any means represent the loss from the body, since 

 of this amount at least 700 grams is due to the oxygen absorbed out of the air, 

 and the actual loss from the body would therefore be approximately 900 grams 

 of water and organic material. 



