666 



NATURE 



[July 21, 192 1 



The animals were first given a mixture of amino- 

 acids from casein {i.e. without tryptophan, which is 

 destroyed in hvdrolvsis by acid) to which tryptophan 

 was added; on the twelfth day the tryptophan was 

 omitted, and included once more on the thirty-fifth 

 day. There was growth during the first period, 

 decline in weight during the second period, followed 

 by growth on inclusion once more of the tryptophan. 

 This is shown by the continuous lines in Fig. i. The 

 upper dotted line shows continuous growth on com- 



FiG. I. — After Ackroyd and Hopkins. 



plete mixture. The lower dotted line shows loss of 

 weight in absence of tryptophan. 



Similar experiments have been made by Osborne 

 and Mendel in America. They used the gliadin of 

 wheat as protein. This protein is a complete one, 

 "but it contains very little of certain amino-acids, 

 especially lysine. Adult rats were maintained for 

 quite long periods, so long as 500 days, but young 

 rats capable of growth, though maintained for long 

 periods, failed to grow. 



We may here notice that 

 though the growth of the 

 animal may be suppressed and 

 it reaches maturity in age, the 

 capacity to grow is not lost. 

 Osborne and Mendel illus^ 

 trated this by a photograph of 

 a rat which had failed to grow 

 for 273 days, but resumed 

 growth on being given a suit- 

 able diet. 



The small amount of lysine 

 in gliadin led the authors to 

 regard this unit as essential 

 for growth. In a later ex- 

 periment they added lysine 

 at intervals ; growth took 

 place with the lysine, but not 

 without it. Fig. 2 shows 

 the upward curve of growth 

 with lysine, but no growth 

 "without it, in four sets of rats. 



The effect of lysine on growth was again demon- 

 strated by Buckner, Nollau, and Kastle in the case of 

 chickens living under the natural conditions of a 

 poultry farm. The birds were fed upon grain mix- 

 tures of high and low lysine content ; growth was 

 more rapid on the mixture of high lysine content. 



The element sulphur is present in proteins in the 

 form of cystine, thoue^h it is possible that another 

 sulphur-containing unit is present. Little or no 

 cystine in a protein has also an effect upon the growth 

 of rats. This has been most clearly demonstrated in 



NO. 2699, VOL. 107] 



the case of the protein, phaseolin, of the navy bean. 

 There was slow growth with this protein alone, but 

 normal growth if the protein were supplemented with 

 2 per cent, of its amount of cystine. 



Casein is deficient in cystine. Less casein is 

 required in a diet for producing normal growth ; if 

 extra cystine be included 15 per cent, of casein was 

 required by itself, but only 9 per cent, if cystine were 

 added. 



The amino-acids containing aromatic nuclei are 

 probably essential units of the protein, but it is difficult 

 to carry out a decisive experiment, since all proteins 

 contain phenylalanine, though they may lack tyrosine. 

 There is plenty of evidence that phenylalanine can be 

 transformed in the body by oxidation ; both tyrosine 

 and phenylalanine yield homogentisic acid in cases of 

 alkaptonuria. Totani has shown that tfie almost com- 

 plete removal of tyrosine from the mixture of units 

 yielded by casein made no difference to the growth of 

 rats. There was evidently enough phenylalanine for 

 all purposes. 



The two hexone bases, arginine and histidine, as 

 shown by Ackroyd and Hopkins, are interrelated in 

 nutrition. Absence of both causes loss of weight; 

 absence of either alone lessens the rate of growth. 

 These two workers further showed that these aminow 

 acids are connected with the production of the purine 

 ring in the animal body, i.e. with the production of 

 uric acid. 



The function of the whole group of mono-amino- 

 acids has yet to be determined. Are they all neces- 

 sary? Of glycine we can say that it is not essential, 

 for it is the only amino-acid which the animal can 

 synthesise. 



These results remind us of the well-known experi- 

 ments on the need by plants of all the inorganic 

 elements. Sir Daniel Hall in his "Fertilisers and 

 Manures " gave a striking picture of barley-grains 

 grown on a full food and on foods lacking one con- 

 stituent. We may thus correlate the amino-acid con- 



FiG. 2. — After Osborne and Mendel. 



tent of proteins for the growth of animals with the 

 set of inorganic elements needed for the growth of 

 plants. 



The relative value of various proteins in nutrition 

 has been studied by Osborne and Mendel. In their 

 experience lactalbumin is superior to casein, and 

 casein to edestin. They found that 50 per cent, more 

 casein and qo per cent, more edestin were required 

 to produce the same gain in weight; in other terms, 

 a food containing 8 per cent, of lactalbumin was 

 equal to one with 12 per cent, of casein and 15 per 



