voegtlin: role of vitamines in nutrition 575 



The condition (10) for compensation therefore reduces to - = 1.7. 



a 



When j3/a exceeds that value, and if, as usual, both a and /3 

 are negative, we are led to the paradoxical conclusion that the 

 disc will become stiffer when heated. Nor can the paradox be 

 avoided by supposing that no such materials will be found or 

 that a and (3 depend on the state of stress — both of which pos- 

 sibilities may in themselves be true — for the variable 6 in the 

 differentiation was in fact arbitrary, so that we may restate the 

 conclusion thus: Of two discs having the same Young's modulus, 

 that with the less rigidity is the stiffer. 



Note on the proposed experiments. The experiments referred 

 to in footnote (1) have as their ultimate object the develop- 

 ment of formulas for the stiffness of corrugated diaphragms. 

 In the course of the experiments it is proposed to determine 

 anew a and /3 for a series of materials, and thus to test directly 

 the above paradox. A preliminary group of experiments on 

 flat circular discs, conducted at the Bureau of Standards in 

 July with the assistance of H. B. Henrickson, and in which both 

 the increase in hysteresis and the decrease in stiffness with 

 rising temperature were observed, led to the following progres- 

 sion of materials when arranged in descending order of magni- 

 tude of the latter effect : soft sheet iron, tempered steel, phos- 

 phor-bronze, zinc, aluminum, copper, brass, and German silver. 



The value of - — was about — 6 per cent per degree C. for the 

 o dd 



iron disc, and for German silver it was at small deflections and 



just perceptibly positive at large deflections; intermediate, but 



very small and nearly equal, values were found for the intervening 



materials. 



PHYSIOLOGY. — The importance of vitamines in relation to nu- 

 trition in health and disease. 1 Carl Voegtlin, Professor of 

 Pharmacology, United States Public Health Service. 



The purpose of my lecture is to give you a brief outline of the 

 most recent phase of the science of nutrition ; namely, the impor- 



1 A lecture delivered before the Washington Academy of Sciences, April 28 , 

 1916. 



