Chairman's Opening Remarks 3 



counting technique or by the use of larger experimental 

 animals. There will be advantages also in using one, or at 

 most a few, kinds of animal, since species differences may be 

 surprisingly great. Whereas in normal man 90 per cent of a 

 dose of radioactive-iron is utilized for haemoglobin production, 

 the same figure in the rat or dog never rises above 60 per cent. 



There is also little uniformity in the manner of administering 

 labelled substances. Whereas Whipple and his collaborators 

 feed amino-acids to their dogs and find peak values for free 

 labelled amino-acids in the plasma at 4-6 hours, Borsook 

 uses intravenous injection and finds that the free amino-acid 

 has largely disappeared from the plasma in 10 minutes. Even 

 the method of expressing results is sometimes confusing. 

 Whereas some plasma protein investigators give their results 

 in the form of the proportion of amino-acid in the protein 

 which was derived from the labelled amino-acid in the diet, 

 others give the proportion of total administered isotopic 

 amino-acid which appears in a given weight of plasma protein 

 — and the figures cannot easily be related. 



These inconsistencies which may appear to be of a minor 

 technical nature stand, nevertheless, in the way of an alto- 

 gether wider view of metabolic events. If our discussions, 

 ranging as they will over several important fields and con- 

 tributed to by leading protagonists in each, can serve to 

 smooth out the technical difficulties while at the same time 

 keeping in view the broader principles, the effort made by 

 many to attend the Conference and by the Ciba Foundation 

 to arrange it will be amply repaid. 



