l8o THE ENERGY OF THE LIVING PROTOPLASM. 
days standing, almost completely; dilute sulphuric acid and 
caustic potassa acted in the same way, so that there can be 
hardly any doubt that the active principle is an enzyme. 
Oxidising enzymes appear to be present also in the animal 
body. Saliva produces a blue colour with Wurster's reagent 
(tetramethylparaphenylene-diamine), a fact erroneously taken to 
be a proof of the presence of hydrogen peroxide ; it produces 
further a brown colouration with hydroquinone. B. Salkowski 
found in the blood, Jaquet and also Yamagiwa in the lungs, 
kidneys, and muscles, enzyme-like agencies, capable of producing 
small quantities of benzoic acid from benzyl alcohol and of 
salicylic acid from its aldehyde. (I) But such actions of enzymes 
are always of a very narrow compass ; they belong to very weak 
oxidations of certain benzene compounds, but never to an attack 
upon, to say nothing of a complete combustion of, sugar or fat. 
We must therefore reject also the theory of Traube as wholly 
unsatisfactory. 
It appears singular that the authors mentioned all ignored 
just the most important condition for respiration, i.e., the living 
stale of the protoplasm . Taking a plain chemical start and leaving 
physiology aside, they endeavored to reach a satisfactory expla¬ 
nation, biased by the idea that the albuminous compounds the 
chemist studies in his vials are the same as those composing 
living matter. This erroneous conception still governs the 
minds of many, and by them respiration will never be com¬ 
prehended. 
It was Pflüger who in the year 1876 drew the inference in 
plain and forcible logic that the proteids of the living protoplasm 
are different from those of the dead, and that their chemical 
change into the indifferent common proteids signifies the death 
of the cells. Only those chemical qualities exhibited by the 
living cells can induce respiratory activity. “ Oxygen is not 
made active, but the proteids of the living cells have the 
activity.” Thus, a new foundation was gained, but few physio¬ 
logists took notice of it ; above all, however, Nencki assented. 
Detmcr modified Pflüger’s view, assuming a continuous dissociation 
(1) Jahresb. f. Thierchem., 22 , 387. Also Röhmann and Spitzer : Ber. Chem. 
Ges., as, 567. 
