Febbuary 17, 1905.] 



SCIENCE. 



251 



processes may reach an equilibrium, just 

 as an electrolyte practically ceases to pass 

 a current of electricity unless a depolarizer 

 be present. So in the hydroxylation of 

 proteids, there is needed some substance to 

 disturb constantly, in one direction or an- 

 other, the equilibrium that tends to be 

 reached. The common agent in this is 

 oxygen. Of course oxygen can hardly be 

 the only depolarizer that can promote fur- 

 ther action. Thus, Maze found the pres- 

 ence of levulose conduced to the continued 

 evolution of carbon dioxid in the absence 

 of oxygen, and it is quite pos.sible that 

 levulose took up the role of depolarizer, 

 though Maze does not so interpret his ob- 

 servation. 



In anaerobic respiration insufficient oxy- 

 gen is supplied. Its products that have 

 been most observed and are therefore 

 (though doubtless groundlessly) counted 

 its characteristic products, are carbon di- 

 oxid and alcohol. Indeed, lactic acid seems 

 an equally characteristic though transient 

 product. The fact that hydrogen has also 

 been often recognized among them supports 

 the interpretation of the function of oxygen 

 just suggested, and accords thoroughly with 

 the theory of hydroxylation. In that proc- 

 ess hydrogen atoms from the dissociation 

 of vv^ater would be left free in case there 

 was insufficient oxygen to form HjOg. 



Fourth: But if the organism can get an 

 adequate supply of oxygen, the katabolism 

 continues, some of the most complex pre- 

 vious products breaking up by hydroxyla- 

 tion and thermal cleavage. Among the 

 fragments are undoubtedly some that lose 

 in part those very groups in which sugars, 

 alcohols, fatty acids, etc., are peculiarly 

 rich. These are rebuilt at the expense of 

 such foods, which therefore disappear as a 

 result of respiration. That ethyl alcohol 

 does not persist when oxygen is present 

 may mean either that it is decomposed, or 

 that in its nascent state it is assimilated in 



the rebuilding of proteids, for we have seen 

 how easily acetic acid, one of its oxidation 

 products, can be converted into an amido- 

 acid, glycocoll, and be thus in direct line 

 for reconstructive metabolism. 



This in its fundamental features is the 

 theory I have presented in lectures to ad- 

 vanced students since 1898, though always 

 as more or less a speculation. For various 

 details I am indebted to the recent litera- 

 ture already cited. Because it is capable 

 of explaining the observed facts, which are 

 sufficiently numerous to demand a coherent 

 explanation, I conceive it to be entitled to 

 the dignity of a theory. Time forbids the 

 discussion of details, and many points have 

 been considered that can not be here pre- 

 sented. 



This theory maintains the direct relation 

 of aerobic and anaerobic respiration, whose 

 genetic connection was long since advocated 

 by Pfeft'er. Anaerobic respiration is the 

 primary process in all organisms. Whether 

 aerobic respiration occurs or not depends 

 upon the availability of oxygen. The rela- 

 tion of fermentation to the process is not 

 wholly clear; for although fermentation 

 gives rise to the same products as anaerobic 

 respiration, this may depend in part upon 

 respiratory decomposition, such as has been 

 described, and in part upon digestion, 

 which, as Iwanowsky and Maze think, ren- 

 der the alcohol from sugars available for 

 assimilation. I am inclined to believe that 

 in fermentation we deal with an exag- 

 gerated anaerobic respiration, the active 

 ferments being plants in which zymase is 

 produced in such amounts that it can at- 

 tack sugars outside the organism and thus 

 secure sufficient energy with a minimum 

 destruction of the protoplasm. 



ENERGESIS. 



Finally, I may suggest that for didactic 

 purposes it is desirable to have a word other 

 than respiration to designate the disruptive 



