154 Kafirin 
The Lysine Requirement of Immature Animals. 
The data bring out one fact of general application; namely, 
that lysine is indispensable, even for the maintenance of young 
animals. This point has been in doubt for some time because 
of the difficulty in proving that a diet contains no lysine. Gli- 
adin was formerly thought to lack that particular amino-acid, 
and because of that belief, earlier experimental work on the nu- 
tritive properties of gliadin was assumed to have special signifi- 
cance. Osborne and Mendel (1914) stated that rats maintained 
their live weight unchanged, but failed to grow when gliadin 
formed the sole source of protein in the ration. Their interpre- 
tation was that lysine is necessary for growth, but is not neces- 
sary for maintenance. When somewhat later the presence of 
lysine in gliadin was established, they (1916) recognized the 
element of doubt attached to their earlier pronouncement. The 
behavior of animals receiving their protein in the form of zein 
has also been interpreted as an indication that lysine is not 
required for the maintenance of nutritive equilibrium. Willcock 
and Hopkins (1906) found that mice receiving zein as the sole 
source of protein died in less than 2 weeks. ‘Those receiving 
zein and tryptophane were active after 16 days of zein feeding, 
but had lost weight. Wheeler (1913) obtained similar results, 
but even after fortifying the zein with tryptophane the animals 
constantly lost weight. Similar results are recorded by Osborne 
and Mendel (1914) in their series of experiments. Their animals 
receiving a zein plus tryptophane diet were at a nutritive stand- 
still or lost weight, though they grew rather rapidly on the further 
addition of lysine. 
The precise status of lysine in nutrition remained uncertain, 
however, because of the difficulty in estimating or even detecting 
small quantities of that amino-acid. Recently Osborne, Van 
Slyke, and collaborators (1915) published data indicating no 
inconsiderable quantity of lysine in gliadin. The method of - 
Van Slyke yielded an average result of 1.33 per cent, and the 
direct method of Kossel and Kutscher resulted in the recovery 
of 0.64 per cent of the gliadin as lysine. There is no doubt, 
therefore, that gliadin contains approximately 1 per cent of 
lysine, while kafirin, according to Johns and Brewster (1916), 
