666 Experiments 



1. Respiration. 



In general, the respiration quickens when the pressure is 

 lowered. But nothing is more irregular than these modifications in 

 the respiratory rate. Here the effect of the suddenness of the 

 phenomena is of greatest importance. The animal is startled, stirs 

 about, struggles; it is irritated by the expansion of gases of which 

 I shall speak under the heading of digestion, and all these effects 

 accelerate its breathing. But it often happens that the respiration 

 grows slower and becomes deeper; that is almost the rule at very 

 low pressures. This is noticed particularly when the animal re- 

 mains quiet; agitation has always seemed to me to speed up the 

 breathing. 



In a word, here as in all the other circumstances, lessening of 

 pressure acts the same as asphyxia. We know that in asphyxia in 

 a closed vessel there is also a phase of respiratory acceleration, 

 followed by a phase of retardation in which the thoracic move- 

 ments are made slowly and painfully. The experiments reported 

 in Chapter I also show frequent examples of this respiratory 

 acceleration in animals kept at various low pressures. 



But to show how difficult it would be to include all these facts 

 in a general formula, it is sufficient to study the experiments closely, 

 being careful especially to show by graphs the results in which 

 comparison is difficult. 



In Figures 47 and 48, in which the graphs show only respira- 

 tory movements, and in Figures 49, 50, and 51, in which the pulse 

 rate is also plotted, the direction of the arrows indicates the series 

 of successive alterations in pressure to which the animals were 

 subjected. When the arrow points to the right, the pressure de- 

 creases; towards the left, it increases. Pressures are reckoned on 

 the axis of the abscissae; on the vertical axis are written the num- 

 bers corresponding to the respiratory movements R and to the 

 pulse P. 



Line B (Fig. 47) gives the details of Experiment CCXV, made 

 on a dog. We see that here effects were produced in a simple and 

 regular manner, the number of respirations increasing or decreas- 

 ing inversely as the pressure. 



Line A, on the contrary (Exp. CCXVII, another dog), shows 

 a singular complication; in a general way, the number of respira- 

 tory movements decreases as the pressure decreases. 



We note similar differences with rabbits. While Experiment 

 CCXXV shows a simple relation between the pressure and the 

 number of respiratory movements, Experiment CCXXIV, repre- 



