146 GASEOUS METABOLISM OF INFANTS. 



When isolated nutrients are ingested, the greatest increase has been 

 observed with protein. With fat there is relatively but little, if any, 

 increase. With carbohydrates, while investigators differ as to the 

 quantitative relationships, it has been observed with men in this labora- 

 tory that cane sugar and levulose may stimulate the metabolism to 

 a degree comparable with that resulting from the ingestion of an 

 equivalent weight of protein. On the other hand, lactose — the chief 

 carbohydrate in the diet of infants — has a minimum influence upon 

 the metabolism. 



This criticism of our experiments has, therefore, considerable theo- 

 retical importance, but practically we must consider the fact that 

 the diet of the infant is of such a character as to produce a minimum 

 amount of increase in the metabolism. With infants a large proportion 

 of the protein ingested — some 60 per cent or more — may be stored in 

 the body, and Rubner has shown that this storage does not affect the 

 total metabolism. Since the protein ingested by the infant rarely 

 exceeds 15 per cent of the total energy requirement of the bod}', 1 it 

 can be seen that we may expect from this nutrient only the minimum 

 influence upon the heat-production of infants. Fat has admittedly but 

 a slight influence, while the predominating carbohydrate — milk sugar 

 or lactose — has likewise only a minimum influence. 



On these grounds, therefore, one would conclude that the total 

 nourishment of the infant consists of material which for the most part 

 does not tend to stimulate the metabolism greatly. On the other hand, 

 so keen an observer as Schlossmann 2 states that the effect of the inges- 

 tion of food probably persists for some 18 hours. Practically all of 

 the investigators in metabolism have concluded that with adults, unless 

 the diet is abnormally rich in protein, the metabolism reaches the basal 

 line 12 hours after the last meal. 



In our studies while it was impracticable to secure the metabolism 

 on all of the infants 18 hours after the last meal, an effort was made to 

 find out the length of time required to obtain the minimum basal 

 metabolism after feeding milk. To this end some five or six infants 

 were studied 1, 2|, 5, 9, 12, 18, and 21 hours after food. The difficulties 

 in securing ideal periods of rest exactly coincident with definite periods 

 of time after the ingestion of food are sufficiently obvious to need no 

 special comment here; it is only necessary to state that our evidence 

 is admittedly not so complete as we should like. A critical examina- 

 tion of the data shows us, however, that on the whole the influence of 

 milk feeding upon the metabolism of infants must be very slight. In 

 certain instances the metabolism during quiet periods immediately 

 after feeding is 5 to 10 per cent higher than 18 to 21 hours after, while 

 in others the metabolism 21 hours afterward, even in periods of com- 



^Rubner, Sitzber. K. Preuss. Akad. Wiss., 1911, 20, pp. 440-457. 



-Schlossmann, Atrophie u. respiratorischer Stoffwechsel, Kassowitz Festschrift, Berlin, 1912, p. 31S. 



