316 RESPIRATION. 



cumstances. If it is not intended to record the results graphi- 

 cally, it may be allowed to run about while the respirations arc 

 counted, and careful observations are made as to the respira- 

 tory movements. For more exact observations various methods 

 may be used, each of which is of some value. The first consists 

 in recording the movements of the diaphragm on the kymo- 

 graph, as directed in 9 1. 1 The second and third are so con- 

 trived as to show not only the duration and rhythm of the 

 respiratory movements before and after section, but the extent of 

 the respiratory exchange of air. The apparatus for this purpose 

 is constructed as follows: A large bottle, capable of holding 

 five gallons or more, is closed air-tight with an India-rubber 

 cork, into which the stem of a glass T tube is carefully fitted. 

 Of the two branches of the T tube, one communicates with the 

 respiratory cavity of the animal, by a connector of Indiu-rub- 

 ber and a glass canula secured air-tight in the trachea, the other 

 is left open and can be readily closed with the finger. The 

 bottle also communicates by a second glass tube which passes 

 through its India-rubber stopper, with a Marey's tympanum, 

 the lever of which writes on the blackened cylinder of the kymo- 

 graph. This tube is controlled by a screw clamp. So long as 

 the arm of the T piece is left open, the animal of course breathes 

 the external air freely. On placing the finger against the aper- 

 ture, it begins to breathe the air of the bottle, but inasmuch as 

 the capacity of this vessel is 250 times as great as the respira- 

 tory cavity of the rabbit, it can do so for some time without 

 the slightest dyspnoea, as is proved by the observation that the 

 depressors of the larynx do not come into action. The resist- 

 ance is, however, sufficiently great to affect the lever of the 

 tympanum, the rise and fall of which in each respiratory act is 

 in exact proportion to the quantity of air breathed. The animal 

 having been chloralizcd and both nerves prepared as above de- 

 scribed, a few tracings should be taken of the normal respira- 

 tion. This done, the clockwork is again set in motion and both 

 nerves are divided at the same moment. In this way a tracing 

 (fig. 253) is obtained, which strikingly exhibits the effects of 

 section, both as regards the rhythm and extent of the thoracic 

 movements. 



Another method consists in measuring the quantity of air 

 inspired in a given time with the aid of the apparatus shown 

 in fig. 251. In this way the effect of section on the respiratory 

 exchange can be estimated with much greater precision than 

 in any other, but obviously no information is obtained as to 

 the respiratory movements. 



100. The most important results are as follows : 1. In the 



1 The tracing so obtained is shown in the first (normal) part of fig. 

 255. 



