KARUKK EXPERIENCES OF THK AUTHORS. 59 



EARUER EXPERIENCES OP THE AUTHORS. 



As the result of the first year's experiments, it was found possible 

 to maintain rats in health and apparent nutritive equilibrium over 

 considerable periods of time on a mixture of isolated food-substances 

 containing isolated proteins as the source of nitrogenous intake. For 

 example, one protocol (Chart XXX) shows that a full-grown rat* 

 was maintained satisfactorily in this way for more than 2 1 7 days on 

 glutenin, the animal continuing on this regime at the time when the 

 earlier report was prepared for publication. Rats were likewise main- 

 tained on diets in which other proteins, notably casein alone or in 

 combination with isolated vegetable proteins, formed the sole nitrog- 

 enous food component, over periods of time exceeding any previously 

 reported, at least under conditions in which the "purity" of the 

 dietary substances was carefully maintained unchanged over equally 

 long periods of time. By maintenance we do not merely mean that 

 the animals remain alive. No feeding experiment is to be regarded as 

 successful in fulfilling the nutritive requirements unless the animals 

 approximately maintain their weight and health (or make normal 

 growth if they are at a stage where this is still to be expected). 



Although these apparently successful experiments indicated that 

 the combinations of isolated food-stuffs employed satisfied the nutri- 

 tive requirements of the rats and consequently constituted a com- 

 plete food for the maintenance of mature animals, a prolongation of 

 the observations has led to a less favorable outcome. A continuation 

 of the experiments over longer periods has shown that in every case, 

 sooner or later, the animal declined ; and unless a change in the diet 

 was now instituted within a comparatively short time the animals 

 died. The Charts XIV, XV, XVI in our earlier paper illustrate this 

 very well. The rats 23, 24, 25 were maintained without noteworthy 

 alterations in weight over 130 to 160 days on a constant mixture 

 including a single protein. The animals ate well, as the food records 

 show, until the final period of decline. 



These records can be duplicated, especially in respect to the de- 

 cline, by many others, as for example Charts XLI, XLII, LXXVIII, 

 LXXIX, LXXX, CII, CXV, CXVI appended to this report. The 

 history of rat 71 is particularly instructive on this point. f This 

 animal (see Chart XXX), weighing 257 grams on April 5, 19 10, 

 was put upon a diet containing casein (12 per cent) and glutenin 

 (6 per cent) as the only proteins. Subsequently glutenin alone 

 (16.4 per cent after 69 days and 18 per cent after 104 days) formed 

 the protein of the diet. The rat continued in excellent nutritive 



*The earlier data regarding this animal, rat 71, are given in Publication No. 156, 

 Carnegie Institution of Washington, p. 47 ff. 



jThe earlier data will be found in Publication No. 156, Carnegie Institution of Wash- 

 ington, pp. 47-48. 



