13 



(decrease in body weight, the quantities of nitrogen, sulphur, and phos- 

 phorus which are excreted should be the same as those which are 

 ingested in the food. This should not be construed to imply that the 

 actual elements eaten on one day appear in the excreta of the next day. 

 This is far from being the case. It may require many days, weeks, or 

 even months, for a given particle of nitrogen, sulphur, or phosphorus 

 ingested in the food to reappear in the excreta. It is sufficient, how- 

 ever, for the purpose of establishing the balance between these ingested 

 i substances and those which are recovered in the excreta to assume that 

 the quantities forced out of the body each day when in a normal state 

 are equivalent in all respects to those which are introduced. As an illus- 

 tration, the case of a tube long enough to hold a hundred marbles may 

 be cited. If an additional marble be forced in at one end of the tube, 

 a marble of equal magnitude will be forced out at the other, and thus 

 the balance will be maintained in the tube. So in a state of equilib- 

 rium each molecule or atom of nitrogen, phosphorus, or sulphur enter- 

 ing the body will be represented by a similar molecule or atom of these 

 respective substances forced out of the body. 



Were it practicable in experiments such as these to collect absolutely 

 every particle of emergent nitrogen, for instance, the balance between 

 the entering and departing nitrogen should be complete. In these experi- 

 ments, however, no attempt was made to collect any of the nitrogen 

 except that removed from the body in the urine and feces. This, of 

 course, represents nearly all of the nitrogen excreted, but not quite all. 

 Small amounts of nitrogen are separated from the body in the hair, the 

 nails, and the desquamations from the surface of the body. Thus in a 

 perfectly normal state of the body the sum of the nitrogen excreted in 

 the urine and feces would not represent the total amount ingested in 

 the food. On the other hand, in abnormal states of the body, where the 

 breaking down of the tissues is going on more rapidly than their build- 

 ing up, just the reverse condition would prove true. The same state- 

 ments may be made with reference to the sulphur and phosphorus. 



It is evident, however, that, if a relation can be established between 

 the total amount of these substances entering the food and that leaving 

 the body in the urine and feces, any disturbance of that relation by the 

 addition of an abnormal constituent to the food, such as a preservative, 

 can be easily detected. Therefore, for the purposes of these investiga- 

 tions, the fact that complete collection of these elements from the body 

 is not secured is not a valid objection to the deductions which are made 

 from the data. Nevertheless, it should be pointed out with clearness 

 and frankness that in the conditions in which these experiments were 

 made there are possibilities of error which must not be overlooked. 

 Carelessness on the part of the observer himself in the collection of the 

 excreta, a violation of the pledge in regard to the conduct of life, or an 

 error in analysis would each tend to render the results of less value. 



