THE SOURCE OF MUSCULAR ENERGY. 385 



for days after continued muscular exertion, would be in harmony with 

 such an origin, as they might indicate a gradual replacement of glyco- 

 gen consumed, at the expense of albuminoid material with elimination 

 of urea as a a waste product. Sugars (grape-sugar and maltose) ab- 

 sorbed from digestion or formed from liver-glycogen, are doubtless 

 consumed in the tissues and organs and assist in producing animal 

 heat. Whether muscular tissue consumes these sugars in greater quan- 

 tity than other tissues it is difficult to say with certainty. 



We come now to the second question as to the nature of this de- 

 composition to which we have alluded as oxidation. This question is 

 still contested. The older theory is that the oxygen, taken up by the 

 blood, is given up in the form of active oxygen, or ozone, and by its 

 energetic oxidizing power burns up or oxidizes the carbon and hydro- 

 gen of the fuel-material, with formation of carbonic acid and water. 



The newer theory is that the decomposition processes are essen- 

 tially fermentative in their character ; that under the influence of 

 appropriate ferments the substances combine with water, splitting up 

 into simpler and simpler products with evolution of heat or force, as 

 is the case with all fermentative changes. The oxygen present in the 

 arterial blood gives these processes the character of fermentative 

 changes in the presence of oxygen ; secondary oxidation takes place, 

 as in putrefaction in presence of air, the final products being mainly 

 carbonic acid and water, as also is the case in putrefactive processes. 



Some of the objections raised to the older theory are that we know 

 of no similar changes produced by ozone in watery solutions, such as 

 exist in the animal organism ; that the oxygen obtained from the arte- 

 rial blood under the air-pump contains no ozone. Also certain com- 

 pounds are found in the blood and tissues which are essentially deox- 

 idized products, which could not be supposed to exist in the presence 

 of ozone, but the presence of which accords with the supposed fermen- 

 tative character of the processes (Hoppe-Seyler). The fact that the 

 evolution of carbonic acid from the contracting muscle is in great part 

 independent of the presence of oxygen at the time would harmonize 

 also with such a fermentative character of the changes, as carbonic 

 acid is the product of many fermentative changes out of the presence 

 of oxygen, as, for example, of the alcoholic fermentation of sugar. 

 Matteucci's supposed storing up of oxygen in some form of combina- 

 tion in the tissues would then be interpreted rather as the storing up 

 of fermentable substances (like glycogen) rich in oxygen. The com- 

 bustion theory, on the other hand, would seem to demand that the evo- 

 lution of carbonic acid and consumption of oxygen should be simul- 

 taneous, which is apparently contradicted by the experiments of G. 

 Liebig, Matteucci, and others above mentioned. It would exceed our 

 limits to enter more fully into a discussion of these two opposing 

 theories. The conflict between them is still in progress, and new evi- 

 dence is constantly accumulating. Both theories agree in this, that 



TOL. XXIY. 25 



