RECENT ADVANCES IN SCIENCE 379 



determinations of the minimum daily ration of any substance 

 which will just protect an experimental animal from scurvy, 

 under the conditions of the experiment, and by comparing the 

 values so obtained for the unpreserved and the preserved 

 material, it has been found possible to determine whether there 

 is any loss in antiscorbutic power during the preserving pro- 

 cess. 



According to Drummond {Biochem. /., 1919, 13, yy) an ade- 

 quate supply of all three accessory food factors (r) Fat soluble 

 A, (ii) Water soluble B, and (iii) water soluble C (the anti- 

 scorbutic factor) is essential for the well-being of higher 

 animals. The striking difference in properties between these 

 various vitamines is illustrated by an investigation by Zilva 

 (Biochem. J., 19 19, 13, 164) in which it is shown that the Fat 

 soluble factor A in butter is inactivated by exposure to ultra- 

 violet light for eight hours, while the other two are not destroyed, 

 although the butter itself is so profoundly affected as to be 

 bleached and unfit for consumption. 



Drummond (loc. cit. p. 81) also has shown that the growth- 

 promoting factor A in animal fats is not so stable to high 

 temperatures as has been assumed, that contained in butter 

 or whale-oil being destroyed by exposure to a temperature 

 of ioo° for one hour : the substance could not be identified 

 with any known components of fats, such as cholesterol, 

 phosphatides or pigments, and it is suggested that it may 

 be of an enzymic nature. 



Although it is commonly stated that stinging-nettles con- 

 tain formic acid, the statement rests on somewhat slender 

 evidence furnished by Gorup Besanez, who in 1849 obtained 

 a slightly acid solution by distilling an aqueous extract of 

 stinging-nettles with phosphoric acid. Since then a number 

 of observers have obtained similar distillates by boiling various 

 plant parts with water or by steam distilling them, and it 

 cannot be accepted as proved that the formic acid obtained by 

 Gorup Besanez really came from the stinging hairs of the 

 nettles. To establish the presence of this acid in the hairs, 

 Dobbin (Proc. Roy. Soc. Edin., 1919, 39, 137) has recently 

 employed a somewhat ingenious method : he impregnated 

 filter-paper with barium carbonate by soaking it in 2 per cent, 

 baryta water and exposing it to the air ; taking the paper in 

 gloved hands, he pressed it on the upper and lower surfaces of 

 a large number of leaves of growing nettles. Dealing in this 

 way with several hundred leaves, the liquid expelled from 

 a very large number of stinging hairs was collected. The 

 paper was then extracted with water and the filtered extract 

 distilled with phosphoric acid ; the distillate was treated with 

 lead hydroxide to convert the acid into the lead salt, and 



