EESPIEATORY KHYTHM 497 



them exhibit the characteristic rise and fall of the classical Cheyne- 

 Stokes phenomenon (Fig. 234). 



On trephining the carapace of such an animal, opening the 

 pericardium and ligaturing the pulmonary artery and the two 

 aortae with a single thread, so as to arrest the circulation, the 

 respiratory phenomenon continues; the pauses lengthen, the 

 groups shorten, so that the periodicity of the rhythm becomes 

 more marked. 



When these hibernating tortoises are made to breathe in- 

 different gases such as nitrogen and hydrogen, instead of air or 

 pure oxygen, the periodic respiration continues to be of the same 

 character; dyspnoea is entirely absent, while the number of 

 respirations in the time unit becomes much less. Eespiration 

 with indifferent gases may be kept up for a long time, without 

 cessation of life in the animal. Thus, e.g., a tortoise continued to 

 breathe for two days in an atmosphere of pure nitrogen. 



None the less, protracted respiration of asphyxial or toxic 

 gases, such as carbonic acid and carbon monoxide, does suppress 



FIG. :234. Periodic- respiration in hibernating tortoise. (Fano.) Pneumograms obtained by 

 letting animal breathe from small receiver, connected with a writing tambour. 



periodic respiration in the hibernating tortoise. ~In certain cases 

 carbonic acid produces an inclination to dyspnoea, but only of 

 brief duration. In all cases, whether suddenly or after a short 

 time, the pauses become longer, the groups of respirations less 

 frequent and smaller, until they die out. A water tortoise 

 breathed 18 litres of carbon monoxide for 36 hours. It was 

 removed from the apparatus after its breathing had ceased for 

 about an hour ; yet it was still alive, and after a little time began 

 to breathe again and to move spontaneously. When killed and 

 dissected it showed the most unmistakable signs of carbon 

 monoxide poisoning. 



When a hibernating tortoise is chloroformed, there is a rapid 

 and progressive diminution in the groups of respirations till 

 absolute standstill of the respiratory centres is obtained. Chloro- 

 form, the " reagent for vital excitability," as it was termed by Cl. 

 Bernard, attacks the innermost conditions of the activity of the 

 nerve-centres, removing from the respiratory centres in a short 

 time their capacity to liberate the energy which they accumulate 

 by the accustomed paths. 



VOL. I 2K 



