8o Intracelhilar Proteins [Sept. 



stituents and chemistry has made clear many points in the physiol- 

 ogy of these units. It is true that in general the chemist has 

 studied these Compounds by extracting cells in mass, whereas the 

 histologist is more concerned with their identification in the cell 

 itself ; biit the werk of one Supplements that of the other. 



Another purely biological problem which enlists the efforts of 

 the biochemist is the problem of heredity. We know that the chro- 

 mosomes are the carriers of the hereditary characters and that they 

 are rieh in nuclein or nucleic acid, but the nature of the particular 

 particles of these chromosomes which convey the characters is 

 evidently a problem in their chemical arrangement. Nageli's Classi- 

 fication of idioplasm as " heredity-conveying " protoplasm and his 

 idants or chromosomes, ids or visible chromatin granules, idioplasts 

 or pangens, determinants or invisible molecular aggregates, is an 

 example of the way in which pure biologists resort to chemical lan- 

 guage to explain their conceptions of this problem. 



These two examples serve to illustrate how closely the great 

 biological problems are bound up in the chemistry of the cell pro- 

 teins and suggest fields for our activity. It will therefore be evi- 

 dent, I think, that all biologists are concerned in further extensions 

 of our knowledge along the following important lines : .first, the 

 nature of the protein molecule; second, the condition of proteins 

 in the cell; third, the nature of protein Compounds. I have there- 

 fore divided my discussion under these heads with the view of 

 summarizing our present knowledge. 



The nature of the protein molecule. The work of investiga- 

 tors culminating in the now classical work of Fischer on the Poly- 

 peptids, has shown that proteins are essentially alike. We classify 

 them on the basis of minor differences rather than on any molecular 

 structure. Taylor has carried the synthetic processes still further 

 in his investigation of the manner in which amino acid cleavage 

 products may, by the reversible action of trypsin, be carried to the 

 synthesis of a Compound of undoubted protein nature and essen- 

 tially like Protamin. 



We now can see a reason for the amphoteric character of the 

 protein molecule in the presence of side chains of basic (NHg) 

 and acidic (COOH) natures. The proportions of these determines 



