28o LIFE : OUTLINES OF GENERAL BIOLOGY 



though invisible to our eyes, is chemically active and affects the 

 photographic plate, has a great influence in promoting growth and 

 preventing rickets in rats whose diet is partly deficient in the 

 necessary vitamin. 



A very remarkable discovery recently made is that if rats kept 

 on a deficient diet and not fortified by ultra-violet light are fed 

 with the flesh of other rats which have been treated with the 

 ultra-violet rays, they thrive and escape rickets. Still more remark- 

 able is the discovery just announced by Steenbock and Black: 

 that if the food-ration, known to be deficient in the rickets-prevent- 

 ing vitamin, is exposed to ultra-violet light before being fed to the 

 rats, it mysteriously becomes adequate and sufficient. It seems 

 that ultra-violet light can bring about formation of the vitamin 

 from a known chemical substance, ergosterol, a complex solid 

 alcohol widely distributed in plants and animals, but nouhere very 

 abundant; but it is still too soon to jump to so definite a con- 

 clusion. Indeed, the discoverers are inclined to abandon the idea of 

 a definite rickets-preventing substance, and to suppose that some 

 form of radiant energy is the active agent. But it is difficult to 

 picture this in terms of modem physics. 



A ViT.^MiN IN Development. — On general grounds great caution 

 should be exercised in naming new vitamins, which have not been 

 isolated or chemically determined. For a vitamin is little more 

 than a name for a hypothetical substance whose absence from the 

 food is followed by certain evil results. But there has been some 

 recent evidence of the existence of a new fat-soluble vitamin E, 

 a substance necessary in the food-supply of the mother if the 

 embryo is to complete its development. It has been called the 

 vitamin of reproduction. 



The new vitamin is abundant in the ether extract of wheat 

 embryos and in dried leaves of lettuce. It occurs unhurt in the 

 carefully desiccated leaves of alfalfa and pea, in seeds like cotton 

 and Indian com, in some fmits like bananas, in egg-yolk and many 

 animal tissues. If twenty-five milligrams of wheat-germ oil be 

 mixed daily with the food of a rat that is with young, the develop- 

 ment of the young ones is very successful and normal birth results, 

 but this will not be the case if the hypothetical substance is not 

 present in the diet. Even five times as large a quantity of some 

 other oil, such as peanut and flax-seed oil, with little vitamin E, 

 will not compensate for the absence of the so-called vitamin of 

 reproduction. 



PrzzLi.NG Nutrition. — Could one not fatten stock on waste-paper ? 

 This question is suggested by Dr. L. R. Cleveland's success in 

 rearing white ants or termites on a diet of pure cellulose. As a 

 matter of fact they fed on Whatman filter-paper which had been 

 extracted in hydrochloric and hydrofluoric acids and in ether. 



