THE CONSTKUCTION OF PROTEINS 173 



reduced by the formaldehyde, part of which combines with 

 the resulting product to form hydroxylamine and later 

 formaldoxine, which is then converted into formamide. 



The view of the construction of protein from amido- 

 compounds and carbohydrates, though of course only 

 hypothetical, associates certain processes which apparently 

 occur in nature. Its formation seems to involve the simul- 

 taneous presence in the cells of some amino- or amido-acid, 

 frequently asparagin, and some carbohydrate such as sugar. 

 If shoots of plants which exhibit no accumulation of asparagin 

 during normal growth are cut off and kept in darkness for 

 some time, a gradual accumulation of the amido-acid can 

 be observed. This in all probability is the expression of 

 the decomposition of protein taking place during the life 

 of the shoot, and is presumably a normal occurrence. The 

 reconstruction which would explain its non-accumulation 

 during illumination is prevented by the non-formation of 

 the needed carbohydrate in the darkness. 



The probability of a combination or interaction of these 

 two classes of substance in the synthesis of proteins is 

 supported by the fact that at the active growing points, 

 where protoplasm is energetically formed, and where con- 

 sequently abundant supplies of proteins are needed, neither 

 sugar nor amido-acids can be detected, though they can 

 be traced quite readily up to a short distance below the 

 place where this active growth is proceeding. This fact is 

 easily understood if we admit that protein is constructed 

 there at the expense of these two constituents, supplemented, 

 of course, by the necessary compound or compounds of 

 sulphur. If either of these supplies ceases to be available, 

 the growth of the plant at that point stops. 



Though we have seen reasons for thinking that nitrates 

 and amido-acids form two stages in the normal process of 

 protein construction, we must not conclude that they in- 

 variably do so. In one plant, Pangium edule, which was 

 examined by Treub in 1894, the nitrogen needed for protein 

 construction appears to be supplied in the form of hydro- 

 cyanic acid. In the shoots of this plant, cells occur in the 



