366 CARNEGIE INSTITUTION OF WASHINGTON. 



replace that destroyed in maintenance or used for tissue construction in 

 growth. Thus young rats can for a long time be well maintained on a 

 food with only 2 per cent of lactalbumin ; but if this is reduced to 1 per 

 cent they decline quite as rapidly as on the same diet free from protein 

 and far more rapidly than on a tryptophane-free diet containing zein. 



Investigation of the protein minimum by the use of diets containing 

 different proportions of an individual protein has furnished an explana- 

 tion for the unlike minima for maintenance and growth, respectively, 

 which various investigators of this much-debated problem have 

 reported hitherto for different types of dietaries. The interesting fact 

 has already been brought out that the minimum protein requirement 

 for maintenance is widely unlike in the case of different proteins because 

 of their unlike yield of essential amino-acids. For example, with rations 

 of a certain type less than 3 per cent of lactalbumin serves to maintain 

 nutritive equilibrium as exhibited by stationary body-weight. The 

 same proportion is far too small where either casein or edestin serves 

 as the protein. These latter can be made adequate by increasing the 

 total quantity of protein and equally well by smaller quantities of 

 protein if their amino-acid deficiencies are made good. In the case of 

 casein the addition of cystine alone enables the organism to use a 

 large proportion of the companion amino-acids in the protein for con- 

 structive or other functional purposes without waste. 



The discovery of methods of stunting animals over long periods of 

 time, for example, by feeding incomplete proteins in the ration, use 

 of inappropriate non-protein components in the dietary, limited feeding 

 of adequate diets, alternate exhibition of adequate and inadequate 

 foods, has been followed up by an extension of our experiments in this 

 field. The experiments regarding the capacity to grow after the sup- 

 pression of growth, mentioned in our last report, have given results 

 which disprove the widespread view that the capacity to grow, or growth 

 impulse, is lost with age, independently of whether it has, or has not, 

 functioned during the period actually associated with increase in size. 

 Experiments are at present under way to determine for how long slow 

 growth can be continued and whether or not under such circumstances 

 full adult size will be ultimately attained. Hitherto most of our exper- 

 iments in suppressing growth were limited to animals which had already 

 attained a considerable size. We are now repeating these with much 

 smaller individuals. Furthermore, experiments are under way to 

 deaminate native proteins by chemical methods, so as to determine 

 whether the product of this treatment will maintain an animal without 

 growth, as do lysine-free proteins. It has been made probable by the 

 work of others that in the process of deamination lysine is the only 

 amino-acid destroyed. Our preliminary experiments indicate that this 

 is the case. If these experiments are successful we shall be able, 

 more easily than at present, to prepare foods on which growth can not 



