SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 739 



After birth, the metabohc rate is not a constant, nor does it begin 

 to decHne immediately. In man it rises until about the 4th year, 

 after which it declines continuously except for a slight kink at 12-5 

 years, believed to be associated with puberty. The classical paper 

 in which this peak was observed is that of Dubois, which appeared 

 in 1 91 6, but exactly the same state of affairs is indicated in the papers 

 of Benedict & Talbot; Murlin & Hoobler; Murlin & Bailey; and 

 Marine, Lowe & Cipra. Dubois himself made many measurements 

 of the metabolic rate of children from 6 to 14 years of age, and 

 compared them with those of many other observers for the periods 

 before and after these limits. These papers should be consulted 

 for the relevant literature. In Fig. 165, taken from his paper, the 

 resulting curve is shown, and, as has already been said a definite 

 peak at 4 years of age is to be seen. This curve is in every way 

 comparable with that in Fig. 133, where the data of Gayda on the 

 metabolic rate of the toad are plotted. The figures of Magnus-Levy 

 & Falk, moreover, show the same peak on the basis of carbon dioxide 

 and oxygen determinations. Clearly if this peak were real, it would be 

 expected that infants born some time before term would show a basal 

 metabolism below that of normal infants. This was actually found to 

 be the case by Marsh; Murlin & Marsh; Talbot & Sisson and by 

 Talbot, Sisson, Moriarty and Dalyrymple, whose figures agree very 

 well and demonstrate a little further the earliest part of the Dubois curve. 



Just as in the case of the toad the peak occurs not very long in the 

 life-span after hatching, so in the case of the human being it occurs 

 not very long after birth. But these two organisms are not the only 

 ones for which a peak of metabolic rate has been demonstrated, for 

 Deighton & Wood in 1926, using Capstick's calorimeter, found an 

 exactly similar one in the case of the pig. Fig. 1 66 a shows the 

 results obtained. From birth the pig's metabolic rate rises rapidly, 

 reaching a maximum of 72 calories per square metre per hour at an 

 age of 4 months, after which time it falls away less rapidly than it 

 rose, and this peak holds true also when the heat-production is plotted 

 against the weight. Not only the nature of the curve but also even 

 its general form are in close agreement with the work of Dubois 

 and many others on man, and Gayda on the toad. But Wood and 

 his assistants found that not all breeds of pig gave a peaked curve. 

 If the Berkshire breed was used instead of the Large White, the 

 falling part of the curve appeared but not the ascending part, as is 



