CHANGES IN THE MATERNAL ORGANISM 495 



or wholly prepared by the mother. As stated there, the histo- 

 logical and biological evidence leads us to beheve that the 

 materials, whatever their source and constitution, are in the 

 early stages broken down and partly re-synthesised by the 

 trophoblast, while later in pregnancy they are metabolised by 

 the foetal cells themselves. Granting this, we must further 

 suppose that the maternal duties do not extend to the formation 

 of foetal tissue-components, but are limited to the provision of 

 food and oxygen for the fertihsed ovum, the removal of its 

 waste products, and the preparation of an organ of nutrition for 

 the new-born young. Each of these duties leads to changes 

 in metabohsm, which may, in addition, be excited by special 

 stimuh produced during pregnancy (see p. 491). 



In the provision of nutriment for the embryo, does the 

 mother deplete her own tissues, or is she content to transfer the 

 unorganised substances, which are absorbed from the food and 

 not yet fixed as vital constituents of the protoplasm ? Pro- 

 bably both. In insufficient nutrition the mother certainly gives 

 up organised tissue-products, and, even with a plentiful diet, a 

 period is usually observed during which the mother must draw 

 on her own tissues to account for the loss of nitrogen. On the 

 other hand, it is probable that unorganised substances are also 

 utihsed by the trophoblast, since variations in diet are ap- 

 parently capable of producing changes in the foetus.-' It was 

 noted by the writer and Dr. W. Cramer ^ that abortion oc- 

 curred in three out of six pregnant rabbits fed on a diet rich in 

 carbohydrates during the whole period of gestation. A similar 

 observation is recorded by Cramer and Marshall.'' Wallace ^ 

 states that cows fed on molasses prove to be uncertain breeders, 

 and Heape * that Lincoln sheep fed solely on turnips are 

 specially liable to abortion. 



^ Thiemioh was, however, unable to discover any difference in the consti- 

 tution of the foetal fat, after feeding the mother on widely different fats 

 (see p. 512). 



' See Cramer and Marshall, " A Note on Abortion as a result of a Diet 

 rich in Carbohydrates," Joum. of Econ. Biol., vol. iii. , 1908. 



' Wallace, Farm Live Stock, 1907. 



■ Heape ascribes the frequency of abortion to the fouling of the turnip- 

 roots by mud and excrement, a condition of things which results from over- 

 crowding. See Joum. Roy. Agric. Soc, 1899. 



