Abstract
In a recent paper 1 from this laboratory some success was reported in correcting the failure of rats to reproduce by the addition of yeast to a ration of powdered whole milk. The value of yeast had been indicated by some simultaneous experiments on the white mouse. As was suggested by Miss Wheeler some years ago, 2 the mouse, unlike the rat, cannot grow normally on an exclusive diet of dry whole milk. Of the two limiting factors which she indicated, protein and inorganic salts, the latter appears to be the more important; but on a dried milk ration supplying both of these factors in added amounts the rearing of young has not been generally successful. On a food consisting of dried whole milk 93 per cent., salt mixture 2 per cent. and yeast 5 per cent., we have now obtained a fourth generation. Animals on this food without yeast (98 per cent. milk powder, and 2 per cent. salt mixture, with an additional 0.2 per cent. Fe citrate) become pregnant and young are born, but they are small and scrawny in appearance and usually die within 3 or 4 days. Sometimes no trace is found of these litters, the only evidence being the drop in weight of the female. What constituent of yeast is responsible for the successful reproduction secured by its addition remains to be determined by the work at present under way.
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