THE PROTEINS 



35 



realise the complicated nature of that molecule and the difficulties 

 which beset its investigation. 



The workers in Fischer's laboratory are steadily working through 

 the various known proteins, taking them to pieces, and identifying 

 and estimating the fragments. I do not intend to burden the readers 

 of this book with anything more than a sample of their results, and 

 will therefore only give in a brief table the results obtained with 

 some of the cleavage products of a few proteins. The numbers 

 given are percentages. 





Such numbers of course are not to be committed to memory, but 

 they are sufficient to convey to the reader the differences between the 

 proteins. There are several blanks left on account of no accurate 

 estimations having yet been made. Where the sign + occurs, the 

 substance in question has been proved to be present, but not yet 

 determined quantitatively. Among the more striking points brought 

 out are : 



1. The absence of-glycine from albumins. 



2. The high percentage of glycine in gelatin. 



3. The absence of tyrosine and tryptophane in gelatin. 



4. The high percentage of the sulphur containing substance 

 (cystin) in keratin. 



5. The high percentage of glutamic acid in vegetable proteins. 

 Emil Fischer in his work has sought to make such a list complete, 



and month by month the details are being filled in. He has next 

 tried to discover the way in which the amino -acids are linked to- 

 gether into groups ; and the culmination of his work will be the 

 discovery of the way in which such groups are linked together to 

 form the protein molecule. The last stage he has not yet reached, 

 but it will be interesting to see what progress he has : made in 

 ascertaining how the ammo-acids are linked together into groups. 



D 2 



