278 



VETERINARY PHYSIOLOGY 



Some proteins contain only small amounts of certain 

 essential amino-acids, and a larger supply must be given to 

 supply a sufficient quantity. This is well seen in feeding 

 with casein, which is poor in the sulphur-containing cystin. 

 If too small an amount of casein be given the rate of growth 

 is decreased, but it is accelerated when cystin is added 

 (Chart 3). Similarly, if too small amounts of edestin be given, 



Fig. 141. — To show satisfactory growth of rat upon 18 per cent, of casein 

 (A) and defective growth on 9 per cent, without the addition of 

 cystin, but adequate growth when cystin, in which casein is 

 deficient, was added {B). (Mendel.) 



the small amount of lysin it contains renders it inadequate, 

 and the addition of lysin is required to restore growth. 



A most interesting point brought out in these experiments 

 is the fact that, however long the rate of growth has been 

 checked by an insufficient supply of the constituents of the 

 food necessary for growth, when they are again supplied 

 growth begins again, and proceeds till the normal size may 

 be reached. 



