152 Kafirin 
kafirm formed the sole source of protein supply. In all cases 
this diet resulted in nutritive failure (Chart 1), and accordingly 
kafirin was supplemented with other deficient proteins, gliadin 
and gelatin, in the hope that some clue might be obtained to the 
amino-acid deficiencies of kafirin. ‘These proteins were added 
to the basal ration, in the proportion of 100 gm. supplement to 
each 1,000 gm. of the ration. The addition of gliadin, for a 
‘short time at least, barely sufficed to maintain the live weight 
of the animals; but the addition of gelatin enabled them to grow 
slowly. Both proteins were then added to the basal ration 
(Chart 2) in the proportion of 50 gm. of each to 1,000 gm. of 
the ration, with the result that apparently the animals grew still 
more rapidly than they did when gelatin alone was added. The 
data are illustrated graphically in Charts 1 and 2. 
It is evident, taking the period as a whole, that the rats re- 
ceiving both protein supplements grew more rapidly than the 
rats receiving only gelatin. Isolated periods could be selected 
in which the animals of this latter lot grew as rapidly as the others, 
but probably no especial significance should be attached to that 
point. Two or three obvious explanations for the behavior of 
these rats could be advanced, but the theory chosen tentatively 
was that there are at least two limiting factors in kafirin as a 
source of protein. Gelatin supplies one, and gliadin the other. 
The most conspicuous advantage of gelatin over gliadin as a 
source of amino-acid supply is its much larger percentage of 
lysine. In other respects, however, gelatin is decidedly deficient, 
as it lacks tyrosine, cystine, and tryptophane. Gliadin, on the 
other hand, is deficient in lysine, but contains the other three 
amino-acids in fairly satisfactory proportions. It seemed logi- 
cal therefore to assume that lysine is the first limiting factor in 
kafirin, and that the second is one of the three other amino-acids 
mentioned, tyrosine, cystine, or tryptophane. 
Some of the earlier work concerning the réle of tryptophane 
‘in nutrition has been summarized in an earlier paper (1917) from 
this laboratory. The important réle that cystine plays in nutri- 
tion has been demonstrated by Osborne and Mendel (1915). 
Their data show that when casein is the only protein in the ration 
cystine under certain conditions becomes a limiting factor. Ac- 
cording to Mathews (1915) casein contains 0.8 per cent of sulfur, 
