CULTURE OF PLANKTON DIATOM TIIALASSIOSIRA GRAVIDA CLEVE. 437 



necessary and that this balance had not been attained sufficiently exactly 

 in preparing the solutions. It is quite clear that the artificial sea-water 

 lacks some substance which occurs in natural sea-water, and that a very 

 small trace of this substance is sufficient to make the difference between a 

 considerable and continued growth of the diatoms and practically no 

 growth at all. 



GENERAL CONSIDERATIONS. 



Several instances have recently been described which seem to show that 

 in food material used to support animal life the presence of mmute traces 

 of particular organic substances is essential, if the food material is to 

 maintain the animal body in a healthy state. 



The work of Leonard Hill, M. Flack, G. Hopkins and Casimir Funk * 

 has shown that in the outer layers of wheat and rice there is an active 

 principle which is of essential importance to their value as food material- 

 Young rats and mice would not Uve when fed exclusively upon white 

 flour in the preparation of which the outer layers of the wheat had been 

 removed, whilst those fed on whole meal flour did much better. Pigeons 

 could be successfully fed on bread made of white flour to which an extract 

 of bran and sharps had been added, but when fed on pure white bread all 

 died. Polished rice from which the husk has been removed in the process 

 of polishing, when used as an exclusive diet, produces the disease known 

 as beri-beri. Cooper and Casimir Funk f were able to isolate from rice 

 polishings a substance to which they gave the name vitamine, which 

 effected a rapid cure when given to pigeons suffering from beri-beri. 

 The same substance was obtained from yeast, from milk and from bran. 



Hopkins % has shown that young rats do not grow on an artificial 

 diet composed of pure protein, starch, cane sugar, lard and inorganic 

 salts, but if quite a small quantity of natural milk is added to the 

 diet they thrive. 



Thornton and Geoffrey Smith § have shown that strong growths of 

 Eucjlena viridis in culture media prepared according to Miquel's formula 

 are produced when in place of the organic matter used by Miquel shght 

 traces of amido acids are added to the solutions of inorganic salts. Tyrosin 

 in the proportion of 1 in 24,000 gave an optimal growth. The authors 



* A simiiuary of tins work, as described at the meeting of the British Association in 

 Dundee (1912), will be found in Science Progress, January, 1913, pp. 423-5. 

 t The Lancet, Nov. 4th, 1911, p. 1266, 

 :J Journal of Physiology, Vol. XLIV, 1912, p, 425. 

 § Proceed. Hoy. Sac, B., Vol, LXXXVIII, p. 151, 1914. 



