78 FEEDING EXPERIMENTS WITH ISOLATED FOOD-SUBSTANCES. 



of 150 days, and after this age increase in weight is relatively slow. 

 What will happen to such rats during the later portions of the span of 

 life has yet to be determined in order to answer the question whether 

 this partial starvation in early life has any influence either on 

 longevity or the onset of old age." (p. 314-315.) 



EFFECT OF PARTIAL STARVATION ON NERVOUS SYSTEM. 



Though the period of retarded growth was eventually completely 

 compensated in Hatai's animals, in so far as the weight of the body 

 and central nervous system are concerned, the chemical composition 

 of the brain and spinal cord was not entirely free from the effect. As 

 the result of an extended investigation of the effects of underfeeding 

 on the nervous system, Donaldson* has arrived at the conclusion that 

 one of the characteristics of growth, the change in the water content 

 of the brain, has not been arrested like the increase of the animal in 

 size and body-weight, but apparently accelerated. He states: 



The underfed group are in this character similar to somewhat older ani- 

 mals. Evidence further points to the continued formation of the medullary 

 sheaths with advancing age even in rats which are underfed, i. e., underfeed- 

 ing does not arrest medullation. Underfeeding which stops growth of the 

 body and retards that of the nervous system does not modify the percentage 

 of water in the spinal cord, while it does reduce it in the brain the amount 

 of this reduction being less in the cases where the underfeeding is less severe . f 



With respect to the possible psychological effects of such under- 

 feeding and return to normal diet Donaldson says : 



So far as our tests show, such an experience does not modify the rat's 

 ability to learn, for, by a series of experiments, it has been possible to deter- 

 mine that such a rat can learn to get its food under complicated conditions 

 just as well and as rapidly as a normal animal (Hayes). t 



The preceding facts as to resuscitated rats are recorded here 

 despite the fact that this temporary stunting was produced by under- 

 feeding (rather than unsuitable feeding as in our experiments) 

 because they suggest that the real story of the condition of the 

 animals may perhaps not be revealed by the external evidences of 

 growth. It is not at all impossible that the rats which we have 

 dwarfed for months may have experienced some continued subtle 

 changes in the make-up of the nervous system despite the appear- 

 ance of unchanged youth which they manifest. Measurements of 

 size and weight alone may not suffice to disclose the real physio- 

 logical status of the animal, especially in respect to the development 

 of the nervous functions and structures, which are singularly pro- 



*Donaldson: Journal of Comparative Neurology, 191 1, xxi, p. 139. 



fDonaldson: ibid., p. 169. 



J Donaldson: Journal of Nervous and Mental Disease, 191 1, xxxvm, p. 262. 



