7i8 



THE RESPIRATION AND 



[PT. Ill 



examined the in vitro respiration of chick embryo tissues. His experi- 

 ments have already been discussed in relation to Child's theory of 

 metabolic gradients. If reference be made to Fig. 96, it will be seen 

 that the work led to two conclusions, firstly, that the respiratory rate of 

 the head fragments was greater than that of those from the tail, and 



'calcL-latedfO B.^ H.heab, Murray 0^ 



by <© """ " ^Hasselbalch O2 

 O.N. (^ „„„ „ jShearer02(invifcra) 

 Q Calculabed byCahn 



2 13 14 15 16 

 Fig. 157- 



secondly, that in both cases the rate declined as development pro- 

 ceeded. Reasons have already been given for doubting the significance 

 of the first of these results, but the second remains unaffected, and 

 adds another piece of evidence to the well-established belief that in 

 the chick embryo metabolic rate declines with age. An amount of 

 tissue containing 2-8 mgm. of nitrogen takes up oxygen as follows: 



Day Oxygen in c.mm. 



4 18-50 



5 12-50 



6 5-80 



7 302 

 10 105 



