RESPIRATION OF ISOLATED ORGANS 571 



react with aldehyde groups (as hydrocyanic acid, hydrazine, 

 hydroxylamine, isemicarbazide) or fix amino groups (as 

 formaldehyde and nitrous acid) are all protoplasmic poisons. 

 In opposition to all such hypotheses it must be said that since 

 Franz Hofmeister brought to light a typical protein like 

 eggalbumin in crystalline form, the conception of a "living 

 protein " has lost all its original significance for the chemist 

 (cf. Vol. I of this series, p. 3, Chemistry of the Tissues). It 

 is not in the structure of the protein molecule but in the 

 organization of the cell that the great wall looms up from 

 which unfortunately it can still be called to us: "Nach 

 driiben ist die Aussicht uns verrant." We would not con- 

 tinue: "Thor, wer dorthin die Augen blinzend richtet," 

 but hope and trust that science, forging onward in triumph, 

 will some day force a breach in this wall as well. That, 

 however, this may come to pass from theoretical speculation 

 the author does not believe, however much he may otherwise 

 prize intellectual argument and however highly he may ap- 

 preciate the heuristic value of a hypothesis as a precedence 

 for investigation. 



Methods of Study of the Respiration of Isolated Organs. 

 Unfortunately in physiology it is often necessary to be 

 satisfied to follow to some length phenomena which we do 

 not understand and which we cannot explain. This is ex- 

 emplified by the fact that, although we have scarcely even 

 approached the real nature of the combustion processes in 

 the living body, we have learned at any rate to perform 

 quantitative investigations of the respirations of individual 

 organs. Experimentation along these lines dates as far 

 back as to Carl Ludwig and his school. Although until a 

 few years ago it was possible only indirectly to determine in 

 isolated cases from studies of the energy transformations of 

 the general body what share in these the activities of indi- 

 vidual organs take, to-day this can be directly accom- 

 plished. 



This may be done by studying the changes in the composi- 



