198 THE VITAMINES 



in which S is the duration of life; C, the amount of vitamine that 

 the animal may lose without developing beriberi; V, the amount of 

 vitamine necessary to provide for the metabolism of a given quantity 

 of food; X, the quantity of vitamine in the given diet; K, the con- 

 stant depending upon the quality and quantity of the diet fed. By 

 means of this formula, the vitamine content of various foodstuffs, 

 especially corn, was determined. The figures obtained correspond in 

 general with experience gained by other investigators with the same 

 products. The weak point of the formula is that it shows the pres- 

 ence of vitamine in white rice despite all evidence to the contrary. 

 Aside from this, it is obvious that the survival of pigeons depends on 

 many unknown factors. 



We come now to the consideration of a method, briefly discussed 

 in the chapter on the vitamine requirements of yeast, which was 

 indicative of real progress. This method is based upon the fact 

 that certain yeasts require an addition of substances containing 

 vitamines in order to grow. We have already spoken of the work of 

 Williams (I.e. 128), Bachmann (I.e. 129) and Abderhalden and 

 Schaumann (I.e. 499) all of which led to the development of this 

 method. Soon after, papers were published on the practical applica- 

 tion of the method. Eddy and Stevenson (527) tested the method 

 of Bachmann and found that it was not so very reliable. Thereupon 

 they turned to the method of Williams, by introducing exactly 

 calibrated micropipettes (similar to those used in opsonic index 

 determinations) for drawing up the yeast cell suspension and the 

 vitamine solution, which made the method somewhat more exact. 

 The yeast and vitamine units, with the necessary controls, were 

 deposited on a counting slide and kept in the incubator. After a 

 certain time, the slides were removed from the incubator, stained 

 and the cells counted. The objection to this method is the fact 

 that clumps of yeast cells are often introduced with the cell suspen- 

 sion. In spite of shaking the yeast cell suspension and partial 

 centrifugation to remove the clumps, this objection was not quite 

 overcome and the results were therefore uncertain. Among other 

 substances, Eddy and Stevenson also tested the products isolated by 

 us from yeast in 1912 and 1913 (see chapter on the Chemistry of 

 Yeast) and found them active, while nicotinic acid was inactive. The 

 active substance was not destroyed by heating to 100C., but partially 

 so at 120C. Using this method, more vitamine was found in the 

 mammary vein than in the jugular. 



