COMPARISON OP MILK AND MIXED DIET. 79 



tected even during starvation. This is seen to be true in the series 

 of stunted animals fed on the glutenin mixture in our experiments 

 (p. 72). There is a large field of investigation still open here with 

 important bearings on the problems of retarded growth in man. 

 According to Donaldson* "the progressive diminution of the per- 

 centage of water in the central nervous system with advancing age 

 is to be regarded as an index of fundamental chemical processes, 

 which take place in the more stable constituents of the nerve cells. 

 These processes are but little modified by changes in the environment 

 and taken all together constitute a series of reactions which express 

 not only the intensity of the growth process in the nervous system, 

 but also the span of life characteristic for any given species." Pos- 

 sibly, then, the further study of the nervous system in connection 

 with our experiments may throw light on the phenomena of malnu- 

 trition (which our stunting experiments primarily represent) as well 

 as those of undernutrition or starvation. 



It may be well here to note that the experience of Donaldson f 

 indicates the main features of human growth to be well represented 

 in the albino rat. So good is the essential correspondence that there 

 is every reason to continue the work on this form. The striking 

 difference is that the rat grows some thirty times as rapidly as man. 



COMPARISON OF MILK AND MIXED DIET. 



The failure either to induce substantial growth in young rats or 

 to satisfy completely the maintenance requirement of older animals 

 during very long protracted periods on the mixtures of isolated food- 

 stuffs thus far reported raises the question as to what constitutes an 

 ideal nutriment for a rat. The suitability of mixed diet is beyond 

 question. The favorable experiences with dried milk powder (some 

 of which have been recorded on pages 75 and 76) early directed our 

 attention to this product. Rats were not only resuscitated after 

 nutritive decline and suitably maintained, but also grown from early 

 age on pastes in which the milk powder (with lard and starch) con- 

 stituted the mixture. The commercial brand " Trumilk"! employed 

 by us has been analyzed at the Connecticut Agricultural Experiment 

 Station withthe following results : 



Per cent. 



Water 3-8 



Total solids 96 . 2 



Protein (NX6.38) 25 . 6 



Fat 27.4 



Lactose 37-2 



Ash 6.0 



*Donaldson: Journal of Comparative Neurology, 1910, xx, p. 143. 

 fCf. Donaldson: Journal of Nervous and Mental Disease, 191 1, xxxvn, p. 258. 

 |This product was kindly furnished to us in powder form by the Merrell-Soule Co., 

 Syracuse, N. Y. 



