17G C. M. McCay 



trout, with limited research upon carp and northern pike. 

 During the whole of the past quarter of a century, the white 

 rat has been subject to continuous study. 



Each of these three classes which we used responded 

 similarly to the most important factor that we have ever 

 discovered in extending the span of life. Each can be main- 

 tained for long periods upon diets adequate in quality but 

 inadequate in amount. After long periods of retarded growth 

 each can respond to increased food allowance with resumption 

 of growth. This means that these growth relationships which 

 are known to have a greater influence than any other upon 

 the total span of life and the terminal, chronic diseases of 

 the laboratory rat are subject to study using either insects 

 or fish. Part of the secrets of ageing may certainly be un- 

 ravelled by the use of these lower species which can often be 

 studied in larger numbers and at much less cost than white 

 rats. 



Furthermore, evidence is slowly accumulating in three 

 different nations that the slow growth of dairy calves is 

 reflected in superior life-time performance of the mature 

 animals. This extends the work relating growth and ageing 

 still further because it involves a ruminant that has superb 

 synthetic powers in providing its own needs for water soluble 

 vitamins and essential amino acids. 



The use of insects by the biochemist offers unique oppor- 

 tunities because the cost of such research is modest. Such 

 studies would seem to be especially worth while for scientists 

 who have retired upon modest pensions but retain their 

 faculties for study and research. This would seem to be a 

 natural gerontological research opportunity for practising 

 gerontologists because such study makes modest requirements 

 for space and equipment. The chief hurdle might be the wife 

 of the researcher who would probably not appreciate making 

 pets out of pests. 



Among lower vertebrates, three promising areas have been 

 almost entirely neglected. Some species of fish such as those 

 of the carp family afford especially unique opportunities 



