766 



THE RESPIRATION AND 



[PT. Ill 



done in inactivated horse serum, though in later stages amniotic 

 liquid was used. For comparison some of the figures are included in 

 Table 91 . The curve obviously declines with increasing age, the N.G.R. 

 falling from about 35 to about 5, so that, as can be seen from Table 9 1 , 

 the N.G.R. declines during the embryonic period of the rat from a 

 value equivalent to that of malignant neoplasms and to the very young 

 chick embryo to a value very close to that of the various adult rat 

 tissues. According to one or two of the earhest measurements of 

 Negelein, there is a possibility that the high value of 35 at 0-5 mgm. 

 dry weight may be a peak, to which the curve has risen from earlier 

 lower values. If this turns out to be the case, there will be an inter- 

 esting parallel with the hen's egg, which, according to Tomita's 

 observations, has a marked peak in lactic acid content at the 5th 

 day of incubation (see 

 Fig. 292). Negelein 

 argued that the unfer- 

 tilised egg-cell has pro- 

 bably only a very small 

 N.G.R., so that a peak 

 would be expected. 

 That it comes so early 

 in development is a fact 

 of importance from the 

 point of view of the energy source used by the embryo. Negelein 

 found that the N.G.R. of the chorionic membranes of the rat embryo 

 decHned in much the same way as that of the embryo itself This 

 is shown in Fig. 170, where the age of the membranes, expressed 

 in embryo dry weights, is plotted against the N.G.R., and a few 

 figures are given in Table 91. It is noteworthy that the N.G.R. 

 of the membranes is always much higher than that of the embryo, 

 although it falls in unison with it, if a Httle slower. It maintains its 

 N.G.R. at a level well above that of most neoplasms, so that its 

 hydrolytic mechanisms must be exceedingly powerful. Negelein only 

 did one experiment with the amniotic membrane separately; it gave 

 an N.G.R. of 35-8 at an embryo dry weight of 60 mgm., i.e. slightly 

 above the corresponding N.G.R. of the chorion. 



Negelein's rat embryos gave rather variable results with respect 

 to the O.G.R., for in Ringer solution a measurable amount of lactic 

 acid was formed aerobically, but in serum this only occurred in the 



§50 

 1V5 





J^5 



Trockengewicht eines Embryos (mgr) 

 Fig. 170. 



