CHAP. IX.] THE CONTRACTILE TISSUES. 379 



It will not have escaped the attention of the reader that these 

 experiments are complicated by the exposure of the muscle to what 

 is practically an enclosed space of air. In other words, two methods of 

 experiment are being employed side by side the method of exposure 

 to air as a medium and the method of exposure to blood as a 

 medium. And, as a matter of fact, Ludwig and Schmidt determined 

 that the air in the glass vessel, after an experiment of some hours' 

 duration, had lost some of its oxygen and gained in carbon dioxide. 

 The value of this exchange is, however, relatively slight. Another 

 defect in the method of experiment is also deserving of mention. 

 The blood as it flows into and out of the muscle is necessarily exposed 

 to the air of the 'glass chamber through the membranous walls of 

 the arteries and veins into which the cannulae are inserted. This 

 possible source of error was determined by Ludwig and Schmidt 1 to 

 have no effect upon the analyses as regarded the oxygen which the 

 blood might take up from the air. While to counteract the error 

 as regarded the carbon dioxide which the blood might yield up to 

 the air in the same manner, only those experiments were compared 

 in which the facilities for the escape of it were approximately the 

 same in the rate of flow, and amount of carbon dioxide contained in 

 the blood. 



Although in these experiments the authors above referred to 

 succeeded in imitating to a great extent the changes which go on in 

 the blood in its circulation through muscles, they found that in 

 separated muscles the gaseous exchanges were not so great as in 

 muscles connected with the body, the latter appearing to act more 

 energetically upon the oxygen of the blood. ]n fact, the conditions 

 of temperature adopted by Ludwig and Schmidt but little favour the 

 diffusion of oxygen amongst the tissues and the dissociation of oxy- 

 haemoglobin 2 . 



From the experiments which have been made in the manner 

 described it may be concluded that : 



1. When a muscle through which an artificial stream of blood has 

 been circulating, is deprived of blood, the capacity for doing work is 

 not immediately lost. In the first stages of bloodlessness the 

 irritability increases ; but soon it sinks, at first with rapidity, then 

 more slowly. 



The circulation of blood freed from oxygen, or of the blood 

 obtained from asphyxiated animals, exerts the same action on the 

 irritability of muscles as the absence of blood. 



2. As regards the oxygen absorbed : 



a. The quantity of oxygen taken up by muscle increases 

 directly with the increase in the rate of flow, apart from contraction. 

 Hence the greater proportion of oxygen absorbed in contraction is, in 



1 Op. tit. P. 41. 



2 Pfliiger, Op. cit., Pfliiger's Arch. Vol. x. p. 354. 



