38o THE POPULAR SCIENCE MONTHLY. 



and after muscular action. 2. The examination and comparison of the 

 blood coming to the muscle, and that leaving it, during rest and exer- 

 tion. 3. The examination of the gases given off or absorbed by the 

 active muscle after excision from the animal, and under the influence 

 of artificial irritation. 4. The influence of continuous muscular exer- 

 tion on the respired gases and on the waste products of excretion. 



1. With regard to the changes in the muscular tissue, it has been 

 noticed that the proportion of water in the muscles is increased or the 

 proportion of solids diminished by work, the amount of substances 

 soluble in water is diminished and the amount soluble in alcohol in- 

 creased ; and particularly that glycogen disappears and sugar is in- 

 creased (the latter probably as a product of fermentation at the expense 

 of the glycogen). 



2. Changes produced in the blood are for the most part difficult to 

 trace with certainty ; but, it has been observed that the blood coming 

 from the active muscle contains more carbonic acid and less oxygen 

 than that coming from the resting muscle ; and, further, that the car- 

 bonic acid is increased in greater proportion than the oxygen is dimin- 

 ished. We shall recur to this later. 



3. Investigations into the changes which occur in gaseous atmos- 

 pheres surrounding an excised muscle made to contract under the influ- 

 ence of electricity are interesting and instructive. G. Liebig found that 

 the excised muscle gave off carbonic acid and took up oxygen, but 

 that muscular contraction took place also when the surrounding atmos 

 phere contained no oxygen, carbonic acid being given off, however, 

 in this latter case also. Later observers confirmed these observations, 

 and Matteucci considered, from his experiments in the same direction, 

 that the carbonic acid was not produced at the expense of the oxygen 

 of the surrounding atmosphere, but from oxygen held in some form 

 of combination in the muscular tissue itself. Herrmann found that a 

 portion even of the oxygen absorbed from the air was absorbed in 

 consequence of incipient putrefactions. 



4. Investigations under the fourth head, as to the effect of mus- 

 cular exertion on the general relations of respiration and excretion, 

 have been very elaborate and very numerous. Pettenkofer and Voit, 

 Ludwig and Sczelkow, and others, have investigated the relations of 

 carbonic acid and water given off to food and oxygen consumed as in- 

 fluenced by muscular exertion. Their investigations have shown that 

 the oxygen consumed and carbonic acid and water given off are largely 

 increased by muscular exertion. This bad been noticed as a general 

 fact by Lavoisier a half-century or so earlier, but the experiments of 

 the above-named investigators were carried on with a care and thor- 

 oughness which left little to be wished for in that direction. 



Whether the subject of the experiment be kept on a constant diet 

 during both work and repose, or whether it be allowed to eat and drink 

 according to desire, or even if no food be permitted during the experi- 



