I042 CARBOHYDRATE METABOLISM [pt. hi 



against the diabetic state of the mother. Aron therefore divided the 

 regulation of the foetal blood sugar into two periods, {a) an early- 

 one in which regulation depends solely on the function of the placenta, 

 and {b) a later one in which it depends on the function of the insulin- 

 producing islets of Langerhans as well. The problem of whether in 

 the first of these two periods there is any control of the foetal blood 

 sugar by the maternal insulin, Aron can hardly be said to have 

 solved. Injections of insulin into the mother during the first period 

 certainly lowered the foetal blood sugar, but not as much as the 

 maternal, i.e. 20 to 25 per cent, of the normal instead of 50 per cent, 

 or more of the normal. The conclusion seems justifiable that in 

 period {a) the foetal blood sugar is kept by the placenta at a definite 

 relation with the maternal blood sugar, and this may fall or rise as 

 the latter falls or rises. Aron's conclusion was more complicated. He 

 thought that the foetus, in normal conditions, received from the 

 mother a utilisable form of glucose which it adapted to its own 

 metabolism, and that, when the maternal pancreas was removed, 

 this form of glucose was no longer produced, so that a foetal diabetic 

 state would follow immediately upon a maternal diabetic state. It 

 is difficult to see why this should have followed from his experiments. 

 For further description of the work of Aron and his collaborators on 

 the carbohydrate metabolism of the mammahan embryo, see Section 



I5-3- 



Returning now to Fig. 289 it is obvious that the blood sugar falls 

 in some cases and rises in others as development proceeds. As far 

 as Aron's work went, it appeared to fall in the case of the pig, and 

 to rise in those of the guinea-pig, rabbit, dog and cow. Further points 

 were collected for the rabbit by Snyder & Hoskins but cannot 

 be plotted, as the full data have not been published. These workers 

 state that the foetal rabbit blood contains 33 mgm. per cent, at 

 22 days of gestation and 100 mgm. per cent, at 32 days — it thus rises 

 and approaches the maternal level. Further work on foetal blood 

 sugar levels is urgently required, especially in view of the interesting 

 work of Scott, who in comparing the blood sugar of various mammals, 

 found that it was highest in the smallest ones, i.e. those whose energy 

 expenditure would be greatest (e.g. rabbit 107, guinea-pig 118, 

 rat 138, mouse 245 mgm. per cent, among rodents). 



The effect of glucose in the medium of embryonic cells in tissue 

 culture was first studied by M. R. Lewis who found that its presence 



