The Respiratory Process in Muscle. 



449 



book and has so remained almost to this day, the evidence given by 

 Hermann's eudiometric experiments cannot be accepted on examination. 



It was long ago shown at Cambridge (1) that a large volume of carbon 

 dioxide is expelled from the muscle if rapidly scalded, though it was shown 

 also later (5) that, as du Bois Reymond had found, practically no lactic acid 

 is produced. 



More recently it has been shown (17) that there are two sources of the 

 carbon dioxide expelled on heating ; one is the preformed carbon dioxide held, 

 probably in union as carbonate, which is displaceable by acid but not by heat, 

 while the other is that held in firmer chemical union with protein groups, not 

 displaceable by acid yet dissociable near the boiling temperature. On slow 

 heating, with consequent acid formation, only the former source yields 

 carbon dioxide ; on rapid heating, without acid formation, and at the high 

 temperatures (80 — 100° C.) necessary if heating is to be rapid enough, the 

 firmly held carbon dioxide, and that only, is 'dissipated. Heating, as such, 

 though it may produce a maximum yield of lactic acid, is not accompanied 

 by any fresh production of carbon dioxide. 



Pfliiger (with Stintzing) also supported the origin of carbon dioxide from 

 a previously oxygenated '" giant " molecule by finding that after washing with 

 acid to expel any previously formed carbon dioxide, the giant or inogen 

 molecule broke down on heating to give what they believed to be, and 

 called, "newly engendered carbonic acid." There were grave fallacies 

 however in their technique, and, putting the matter as shortly as possible, 

 when the trial was repeated at Cambridge by better methods it was found 

 that acid applied to muscle at 0° C. expels the preformed carbon dioxide, that 

 the muscle thereafter raised to 40° C. (when the maximal lactic acid yield is 

 given) gives now no carbon dioxide, while heating further to 100° C. gives 

 the normal amount for that temperature as from an untreated muscle (17). 

 Pfliiger had in fact been misled by his failure to recognise the double mode 

 of storage of carbon dioxide in muscle. His "newly engendered" carbon 

 dioxide was the carbon dioxide dissociable from muscle proteins on their 

 coagulation at high temperatures, and it has no relation to the energy store of 

 muscle. 



The last historical support of the inogen theory then, that of the results of 

 heating, breaks down. So far from lactic acid and carbon dioxide arising 

 together from a common precursor, as Hermann and Pfliiger taught, we see 

 that only the particular conditions of experiment determine whether a carbon 

 dioxide discharge appears to accompany lactic acid formation in the muscle 

 or not. 



In a muscle at rest in air, and more rapidly in a muscle in nitrogen, lactic 



