246 



SCIENCE. 



[N. S. Vol. XXI. No. 529. 



if not identical; aerobic respiration, anae- 

 robic respiration and fermentation. Their 

 relations, so far as was known in 1898, were 

 stated by Pfeflt'er in his ' Pflanzen-physiol- 

 ogie' and need not be reviewed. 



THE COURSE OF RESPIRATION. 



^.^ In translating that work Ewart wrote 

 (p. 519) : "The actual course of respira- 

 tion within the protoplast is quite obscure. ' ' 

 Pfeffer himself says (p. 551) : "Our knowl- 

 edge of the inherent protoplastic mechan- 

 ism is too incomplete to afford a sound 

 basis for any theory concerning the phe- 

 nomena of respiration." Fortunately, 

 knowledge in the last six years has broad- 

 ened, and I believe that it is possible now 

 to see pretty clearly what the actual course 

 of respiration is. Perhaps you will say, 

 to foresee rather than to see — but hypothe- 

 sis must outrun demonstration. The ad- 

 vances to which we are indebted for deeper 

 insight are in three fields: (1) the chem- 

 istry of proteids; (2) the course of com- 

 bustion, especially at low temperatures; 

 and (3) the nature of anaerobic respira- 

 tion, and its relation to aerobic respiration. 

 Let me speak of these in order. 



CHEMISTRY OP PROTEIDS. 



A knowledge of the proteids, complex as 

 they are, could only be obtained by a study 

 of their decomposition products. Now 

 there is a very remarkable uniformity in 

 these decomposition products. No matter 

 what the organism from which they are de- 

 rived, no matter how simple they are or 

 how complex, when broken up by the proc- 

 ess of digestion, or by boiling with acids, 

 they yield invariably a series of products 

 which have become in the last few years 

 much better known. These are amino- or 

 amido-aeids; such substances as leucin, 

 tyrosin, arginin, glutamin, glycocoll, etc. 

 ^Materials of this kind are invariably pres- 

 ent, and certain ones are so invarial)ly 

 present that they can be used as the basis 



of distinctive tests for the occurrence of 

 digestion or similar decompositions of pro- 

 teids. This gave a clue to the nature of 

 I)roteids which was followed by several ob- 

 servers, notably by Kossel, in the study of 

 what are believed to be the very simplest 

 proteids, because of the fewness and uni- 

 formity of the fractions into which they 

 break up. These are the protamines. It 

 has become clear from the study of these 

 simple proteids that they are made up in 

 somewhat the same way as the polysaccha- 

 rides, that is by condensation, in this case 

 linking together a series of the amido- 

 acids. This is possible because the amido- 

 acids have a peculiar construction. They 

 are, so to speak, different on different sides. 

 On one side is an acid group and on the 

 other a basic group ; and so the amido-acids 

 can hang together in chains, or even be con- 

 densed or polymerized to make a simple 

 proteid. Among the amido-acids, as in the 

 carbohydrates, there are certain atomic 

 groups, like CH3, CII,, CHOH, CH^OH, 

 COOH, etc., which recur again and again, 

 and in such groups the possibility of re- 

 placing a hydrogen atom or a hydroxyl 

 radicle by some other atomic group is very 

 great. 



Note, for instance, the comparatively 

 simple acetic acid, CH3 — COOH. If we 

 replace one of the three H atoms by the 

 amido group, NII^, we have at once an 

 amido-acid, glycocoll, CH,(NH,) - COOH. 

 which is one of the sorts of material out of 

 which proteids can be made. Out of an 

 alcohol or out of a sugar we may get just 

 the groups CHOH, CH.OH, etc., from 

 which these amido-acids may be construct- 

 ed when nitrogenous substances are present 

 to supply the amido group NHj. Thus the 

 mode of construction of the proteids has 

 been found to show a likeness to that of 

 the complex carbohydrates, and it has long 

 been known that the carbon groups were 

 voiy much alike in both. It further ap- 



