CHAP. IX.] THE CONTRACTILE TISSUES. 383 



being drawn, and the air analysed as it emerges either in whole 

 or in sample (E. A. Scharling 1 , Pettenkofer and Voit). ', 



In a fourth plan (Rohrig and Zimtz) 2 , oxygen is respired instead of 

 air. A rabbit whose lungs have been cleared of nitrogen by the free 

 respiration of pure oxygen for some time, is made to breathe into and out of 

 the same gasometer of oxygen, the bell of which is carefully counterpoised. 

 The oxygen passes from the gasometer to the rabbit, and back again, through 

 water-valves which contain a caustic solution instead of water. In this 

 manner the carbon dioxide formed in respiration is completely absorbed. 

 As the oxygen is used up and the gasometer sinks, the counterpoise is 

 adjusted from time to time in order to maintain the pressure within the 

 apparatus equal to that of the atmosphere. A pump for artificial respira- 

 tion may be readily adapted to this apparatus. 



Effect of In whichever way the experiment is made, the fact 



exercise on is clearly elicited that muscular exertion increases both 

 the gases of the oxygen absorbed and the carbon dioxide excreted, 

 but in 110 ratio of equivalency. To be precise we may 

 take the experiments of Scz.elk.ow, inasmuch as they were specially 

 devised to demonstrate this fact. 



Rabbits were the animals employed. They were fed on a diet of 

 wheat and milk; and the gaseous exchanges of the whole body were 

 determined during rest, and during tetanus of the hind limbs brought 

 on in the manner already described. A study of the numerical results 

 shews that 



1. Much more carbon dioxide is excreted during tetanus. 



2. Usually, but not always, more oxygen is absorbed; but never 

 so much as corresponds with the carbon dioxide at the same time 



exhaled. In other words, the quotient -*= ^ is increased 



O absorbed 



during tetanus. 



It should be observed that all the other conditions of the animal 

 besides those of movement specially contrasted, should be taken into 

 account in these comparisons ; and particularly the condition of food. 

 According to the food the relation of carbon dioxide exhaled and 

 oxygen absorbed is found to vary. This most probably explains the 



CO 



different values assigned to the relationship ~ during a period of 



repose by different observers 3 . 



The above conclusions are illustrated in the following table of three 



, CO n excreted ,, , . .-, 



experiments. Q indicates the quotient g r~5 *-" Q numbers in the 



last column ("experimental errors + N in c.c.") are found by subtracting 



1 E. A. Scharling, "Versuche ii. die Qnantitat der von einem Menschen in 24 

 Stunden ausgeathmeten Kohlensaure." Ann. der Chemie u. PJuirm. Vol. XLV. 1843. 

 Heft ii. p. 214. 



2 Op. cit. Note, p. 382. 



3 See Begnault and Reiset, and Sczelkow, Op. cit. 



