PROTEINS 171 



upon the generality of this statement in connection with cystine, 

 which is the chief amino acid associated with sulphur and the one 

 through which this element enters the protein molecule. Keratin, 

 the chief protein in wool, is 13% cystine; and it has been estimated 

 that a sheep, in order to get the necessary cystine, would have to 

 eat about 60 pounds of fresh grass each day! As a tentative solu- 

 tion to this problem, it has been suggested that perhaps the cystine 

 is synthesized somewhat by the microorganisms in the stomach 

 of the sheep. Or does the sheep really synthesize its own cystine? 

 Whatever the answer may be, we here see some of the interesting 

 sidelights of the questions involved. 



Synthesis of Proteins. — Concerning the formation of proteins 

 there are several different theories, the chief of which may be 

 classified as follows: 



1. That they are made from amino acids 



a. which come from carbohydrates. 



b. which do not come from carbohydrates. 



2. That they are made from some other nitrogen compound. 



The fact that as high as eighteen simple amino acids have been 

 linked together in the laboratory by Emil Fischer (1901) to form 

 simple proteins or peptids, coupled with the fact that when hy- 

 drolyzed the proteins yield amino acids, would almost settle this 

 question. In truth, since the days of Fischer this origin of the 

 proteins is quite generally accepted. The amino acids are built 

 up into proteins by means of enzymes, which can, under the 

 proper conditions, also hydrolyze the protein back to its con- 

 stituent amino acids. The proteins are thus seen to be comparable 

 to the polysaccharides. As the latter are made up of groups of 

 monosaccharides, in like manner the proteins are built up of 

 amino-acid units. Zaleski (1911) showed that in the ripening of 

 peas the protein increased at the expense of the amino acids 

 and the other nitrogen compounds present. 



During germination there is a similar diminution of the protein 

 and an increase of the amino acids present. The problem then 

 becomes one of the origin of the amino acids. 



Whether these are made from carbohydrates or not is a much 



