XVI PROCEEDINGS 



to changes of temperature and to the action of reagents, which of 

 course greatly increases the difficulty of unravelling the nature of 



reactions. Finally they are substance of prodigious complexity 



egg albumen having a molecular weight not less than 12 or 

 15,000. that is to say, there must be several hundred atoms of 

 carbon in the molecule. In spite of these difficulties, however, 

 much progress has been made in the chemistry of the proteins in 

 recent years; and the chief progress has been due to the applica- 

 tion of synthetic methods. The magician under whose direction 

 these methods have been carried out is Emil Fischer. Let us 

 glance at the results. 



When the huge protein molecule is broken up by the action of 

 chemical reagents, such as acids and alkalies, the fragments con- 

 sist of substances which can be analyzed and identified. They are 

 found to belong for the most part to a class of substances known 

 as amino-acids, of which ammo-acetic acid (glycocoll) is a simple 

 example : 



CH 2 NH 2 CO 2 H. 



Now the manner of breaking up of the protein molecule is of 

 such a kind that it is practically certain the parts represent verit- 

 able fragments or are closely related to veritable fragments of the 

 original molecule. The work of Emil Fischer and his students 

 has been devoted to piecing together these fragments in the way in 

 which it seems most probable they ought to be combined. To show 

 the nature of this piercing together let us begin with amino-acetic 

 acid. It contains a group NH 2 CH 2 CO, which Fischer calls 

 glycyl. Now this may be made to combine with amino-acetic- 

 acid so as to yield the following : 



glycyl, -glycine, NH 2 CH 2 CO- NHCILCO 2 H. 

 In the same way we obtain : 



diglycyl-glycine, NH 2 CH 2 CO-NHCH 2 CO-NHCH 2 CO 2 H. 

 And this chain may be lengthened indefinitely. Now by substi- 

 tuting in a similar way other amino-acid groups as leucyl, 

 C 4 H 9 -CH(NH 2 ^CO, other similar compounds are obtained. 

 These compounds are named by Fischer the polypeptides. One 

 of these has been synthesized which contains eighteen amino-acid 

 groups like the above joined together, giving the enormous mole- 



