2 Chairman's Opening Remarks 



people will agree that the result to date is by no means a 

 simplification of oiir former conceptions of how the animal 

 body works. It appears rather that the use of isotopes has 

 uncovered problems of greater complexity than the ones 

 they were intended to solve. Perhaps this is not quite a fair 

 generalization since at least in the case of two elements, 

 namely iron and iodine, relatively clear-cut metabolic pictures 

 have emerged — and for the same reasons, namely that the 

 body reserves of both elements are relatively small, and in 

 each case one metabolic pathway predominates over all others. 



In the case of almost all other elements and especially, 

 of course, with compounds of carbon complex interconnected 

 chains of biochemical events have come to light. Where 

 these chains cross and so-called "metabolic pools" exist, the 

 investigator's field of interest is necessarily broadened beyond 

 that of his immediate problem; for example, the expert in 

 porphyrin synthesis is compelled to take an interest in the 

 broader field of amino-acid metabolism. It seems that more 

 than ever before the specialist has to pay attention to his 

 general biochemistry, and herein presumably lies one reason 

 why he welcom.es such an opportunity as this to meet experts 

 in other branches of biochemistry. 



The second reason arises from the fact that the literature is 

 remarkably disjointed and incomplete, and it is extremely 

 difficult for the reader to correlate the findings of one tracer 

 user with those of another. For instance, in spite of du 

 Vigneaud's demonstration that doubling the dietary level of 

 methionine in the rat increases the proportion of amino-acid 

 oxidized nine-fold, some workers still employ doses of labelled 

 compounds which are comparable to the dietary intake. 

 Others use the dubious procedure of starving or otherwise 

 depleting their animals beforehand in order to enhance the 

 isotope uptake. Far too often, also, samples are taken — 

 especially of blood — which are large enough to disturb signi- 

 ficantly the physiological balance. 



These difficulties are all avoidable by the preparation of 

 labelled material of high specific activity, by refinements in 



