Neglected Areas of Nutrition Research 181 



determine if the young born late in the hfe of a mother 

 niiglit produee young with a longer potential life. No results 

 have come from this study after several years but a few rat 

 mothers have reproduced when past the age of two years. 



If one turns from the rat to examine some of the other 

 common laboratory animals such as the Syrian hamster, the 

 rabbit and the guinea pig, one finds that these have some 

 assets but probably less use than the rat. The hamster would 

 seem the best since it grows old at about the same rate as the 

 white rat. Two studies with this species have indicated that 

 they have a mean life-span of about three months longer 

 than the white rat. Furthermore, the male seems to live 

 longer than the female of this species although this may have 

 been some accident in relation to the stress of the female of 

 this species when it has young (McCay, 1949). 



The rabbit has not been used for the study of ageing 

 because of its long span of life and poorly defined nutrition. 

 The habit of the rabbit in eating its night excreta makes it 

 difficult to study in the nutrition laboratory since animals 

 must be either collared or the complications from the ingestion 

 of products created in the intestine be faced. Long ago, 

 Metchnikoff maligned the large intestine and considered it a 

 liability in relation to life-span. When the waves of science 

 turn their interest towards the large intestine again the 

 rabbit may be the animal of choice since it both creates 

 nutrients within this organ and carries on a substantial 

 absorption from it. 



Both the rabbit and the guinea pig have rather too long- 

 spans of life to interest those who must hurry to solve the 

 problems of old age. Furthermore, both of these species are 

 subject to epidemic diseases. With the potential use of newer 

 marker substances such as chromic oxide and titanium oxide 

 these species may prove especially valuable in studies of 

 intestinal absorption. The rabbit seems unique because it 

 maintains a much greater acidity during gastric digestion than 

 do other species such as the dog, and because the rabbit can 

 adapt itself to a wider range of foodstuffs than even the rat. 



