144 METABOLISM 



experiments, the working up of amides takes place in light. We have still to 

 inquire, however, whether this is possible in darkness, and Hansteen's (1898) 

 researches have shown that this is indeed the case. 



Hansteen provided the plants he experimented on with carbohydrate 

 and nitrogen, either by adding these bodies to the culture solutions {Lemna 

 minor) or by injecting the solutions into the plant through a wound. It is diffi- 

 cult to see how it was possible to exclude micro-organisms in the first case. 

 Moreover, unfortunately, he maintained his experiments for only a few days, 

 so that it was impossible to arrive at any conclusion as to whether continued 

 growth could go on under these conditions. In addition he employed exclu- 

 sively microscopic methods for determining the presence of proteids, viz. by 

 iodine or Millon's reagent. It is well known that such evidence, especially if 

 quantitative in character, is extremely unreliable. Although Hansteen's 

 experiments cannot be considered as free from doubt, we must quote his results 

 here for want of better. Perhaps Effront's (Green- Windisch, 1901, p. 166) 

 statements, which tend to show that asparagin accelerates the action of diastase, 

 are of importance in deciding as to Hansteen's work (p. 151). [Reinhard and 

 SuscHKOFF (1905) have still further called in question Hansteen's results.] 

 Hansteen found : — that in the dark, proteid was produced from urea in the 

 presence of cane sugar just as well as with glucose ; that asparagin, glutamin (and 

 also, as previously mentioned, ammonium compounds) formed proteid only in 

 presence of glucose ; that proteid was formed from glycocoll only in presence of 

 cane sugar ; that as a rule no proteid was formed from nitrates, leucin, alanin, 

 creatin, together with the carbohydrates experimented on, although there are, 

 doubtless, other carbohydrates whose presence may make such a trans- 

 formation possible. 



The chief result which Hansteen arrived at, viz. that in the dark proteid 

 is synthesized from amides and carbohydrates, has been confirmed by Maliniak 

 (1900) by quantitative analysis. He observed, on supplying asparagin, that 

 synthesis of proteid took place in the dark in maize seedlings which had been 

 deprived of their endosperm, and also in etiolated leaves of Faba. The data ad- 

 duced to prove these facts are by no means very convincing, and the experiments, 

 as is often the case, were carried out on too miniature a scale. In opposition to 

 Hansteen, Maliniak found synthesis of proteid from asparagin taking place 

 just as well in the presence of glucose as of cane sugar. It has been shown also 

 that synthesis of proteid takes place in the dark in resting and also sprouting 

 bulbs, tubers, and roots, without any absorption of nitrogen from without, 

 and without any increase in nitrogen ; this has been demonstrated recently 

 in a series of researches by Zaleski (1901) and Iwanoff (1901 a) who employed 

 exact methods of chemical analysis. Whence these proteids arose is not 

 certain, but in every probability from amides. [In young seeds, also, Zaleski 

 (1905) has proved the synthesis of proteid from albumoses, amido-acids, amides, 

 and organic bases in the dark.] 



It may be seen from these remarks how little we really know on these 

 problems, and how desirable it is that some one should produce a really * clas- 

 sical ' work on the subject, for it is impossible to give a complete picture of 

 the process of nitrogen assimilation based on such literature as we have been 

 hitherto considering. A complete exposure of the numerous contradictions 

 occurring in the literature at present available cannot be undertaken at present 

 and hence much research, which may afterwards turn out to be of the utmost 

 importance, has not been referred to at all. 



Just as in the case of the carbon and nitrogen, so also the materials of the 

 ash are * assimilated ' in the plant ; the majority of them, at least, are 

 probably built up into organic compounds. Since, however, we are for the 

 most part completely in the dark as to which elements of the ash are of service 

 in the assimilation of organic substances, a discussion of the process of assimi- 



