216 RUTH WHEELER 



derhalden^^' in getting nitrogen equilibrium in dogs by adding to 

 'incomplete' proteins or their digestion products the amino-acid 

 radicals missing from their food likewise supports such an as- 

 sumption. The more striking are the experiments described 

 by Osborne (cf. Science, N.S., vol. 37, p. 185, 1913) who has also 

 found that the addition of trj^ptophane to zein prevented decline 

 in weight of rats for a very considerable time. Apparently the 

 animal body cannot manufacture cyclic compounds, nor can it 

 maintain itself on food entirely devoid of tyrosine or tryptophane. 



Monotony of diet appears to be of little importance as a det- 

 riment to the nutrition of white mice, provided the diet is an 

 otherwise sufficient one. Even after six months' feeding with 

 precisely the same food they ate as liberally and as eagerly as 

 did those kept on mixed foods. Anorexia seemed always to 

 follow rather than to precede a loss of weight and to be the result 

 rather than the cause of the decline. Mice on inadequate diets 

 ate an average of one to one and one-half grams of food per day 

 until they became ill — in appearance at least. 



Growth is different from maintenance in its nutritive require- 

 ments. The most successful of the foods discussed above, for 

 example, one containing casein + 'protein-free milk,' although 

 satisfactory for adult animals, allowed only a minimal growth in 

 small mice. Osborne and Mendel's rats grew as fast on it as on 

 mixed food; mice, on the other hand, did little more than main- 

 tain themselves. Mice four to six weeks old, weighing 8 to 12 

 grams, seemed able to live on this food indefinitely; two survived 

 six months with no sign of ill health; they were plump, smooth- 

 coated, and normally active without undue restlessness, but they 

 did not grow. Another mouse, for example, gained 4 grams in 

 forty-three days less than one-third as much as the controls on 

 mixed food; it continued to grow slowly however and in 140 days 

 had gained the 8 grams for which the controls required two 

 weeks. This is typical. Some of the smallest ones did not grow 

 at all, were feeble and had a dwarf-like appearance. One gained 

 only 2 grams in fifty-five days; in ten days on a mixed diet it 



'•■' Discussed in Abderhalden's Synthese der Zellbausteine in Pflanze und Tier, 

 p. 61, et seq. 



