152 THE AMINO ACIDS 



whereas gliadin is deficient in glycocoll and lysine and 

 fails to promote growth, it is reasonable to assume 

 that the low content of lysine in gliadin is responsible 

 for the failure of white rats to grow. On the other 

 hand, lysine is apparently not essential for mere main- 

 tenance. Another conclusion which may be drawn 

 from these experiments is that the organism is unable 

 to synthesize lysine, although glycocoll may be syn- 

 thesized with apparent ease, as has been shown in 

 previous pages of this book. Growth means the for- 

 mation of new tissues and in the absence of sufficient 

 lysine the construction of new tissue does not occur 

 readily, or at least proceed at the normal rate. The 

 inference that lysine is concerned with the function 

 of growth may be tested from another viewpoint. If 

 the animals fed with gliadin, lacking in lysine, show 

 a failure to grow the addition of lysine to gliadin 

 should be followed by a resumption of normal growth. 

 Such trials have been made by Osborne and Mendel 

 and the results obtained are most strikingly seen in 

 the following curves. [See Fig. 10.] Failure to 

 grow on gliadin as the sole protein is first shown in 

 the curves followed by a period of growth when 

 lysine was added to the diet. The subsequent with- 

 drawal of the lysine is followed in each instance by 

 a cessation of growth. If lysine is added again growth 

 is again resumed at a normal, to cease again when 

 lysine is taken away. These results lead to the con- 

 clusion that lysine is indispensable for the functions 

 of growth. Data collected by Osborne and Mendel 



