SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 



709 



mained some five times greater as far as Lussana followed it. Here, 

 of course, the effects of muscular movement are coming into play, 

 and Lussana's figure reminds us that, towards the end of embryonic 

 life, the concept of "basal" metabolism becomes important. During 

 the early stages, the embryo can be considered as under basal con- 

 ditions, except for the fact that it is constantly absorbing nourish- 

 ment, because the factor of muscular activity is not operating. The 

 metabolic rate of the echinoderm gastrula, for example, needs no 



c 0- 

 o 



'3 0- 



o 



a 

 jj 



ro 0. 

 ■q.0 



cco 



Day of Incubation 



Fig. 149 



Day after hatching 



such correction. In any case it is not easy to say whether the general 

 notion of basal metabolism can be applied to an embryo at all, and 

 caution must certainly be used with respect to late stages where 

 increasing cardiac activity and muscular movements in the amniotic 

 cavity may affect the readings, A fact which obviously confirms 

 these interpretations of Lussana's figures is that, during the hatching 

 process, the respiratory quotient steadily rose until it reached unity 

 3 days after the chick had come out. Fig. 149, taken from Lussana, 

 demonstrates this, and shows the transition from the characteristic 

 fatty respiratory quotients of the last week of incubation to the 

 state of affairs in which much carbohydrate is being used for 



