xiu RESPIRATORY RHYTHM 471 



The simplest case of tachypnoea occurs in dogs, under perfectly 

 normal conditions, during the hottest days of summer. The 

 accelerated rhythm, which causes an abundant evaporation of 

 water, is, in this case, a protection against an abnormal rise in 

 temperature of the blood, rather than against the accumulation of 

 carbonic acid there (Richet). The thermal excitation of the 

 rutaneous nerves is probably in this case the sole condition acting 

 renexly upon the bulbar centres, so as to determine tachypnoea 

 (Gad). 



Under all other contingencies in which there is already an 

 abnormal rise in the temperature of the blood, as in fever due to 

 any cause, the phenomenon of dyspnoea is much more complex : but 

 one of the fundamental conditions that determines it is certainly 

 the abnormal rise of excitability in the centres, due to the 

 heightened temperature of the blood that circulates in them. 

 Goldstein demonstrated this in 1872 in Tick's laboratory. In 

 order to avoid rise of general temperature in the animal, he 

 surrounded the carotids with two little metal sheaths, with double 

 walls, within which he circulated water warmed so as to produce 

 febrile temperature in the pharynx, while the rectal temperature 

 remained steady. There was at once a rhythmical acceleration of 

 respiration (tachypnoea) in the animal, due solely to the heating of 

 the blood circulating in the head, which raised the excitability of 

 the bulbar centres (particularly of the inspiratory centres). In 

 fact, under these conditions it was found impossible to produce 

 apnoea (which we shall discuss elsewhere) with artificial 

 respiration. 



In face of these facts it seems indubitable that the pulmonary 

 ventilation, determined by the dyspnoea due to muscular fatigue, 

 which is excessive as regards the chemical needs of the tissues, 

 may and should be explained, at least partly, as an effect of the 

 increased excitability of the bulb, consequent on increased tempera- 

 ture of the blood. The genesis of febrile dyspnoea is highly 

 similar. 



Jappelli has recently (1906), from his experiments on man and 

 other animals (dog, rabbit, pigeon), demonstrated a fact which 

 tends to explain many forms of polypnoea in muscular work 

 (running, jumping, etc.) in a different way to those heretofore 

 considered, i.e. independent of the chemical or thermal changes in 

 the blood which irrigates the respiratory centres. He saw that 

 there is in the respiratory nerve centre a distinct tendency to 

 synchronise its rhythmical and alternate impulses with the 

 external rhythmical impulses, which are eventually transmitted to 

 the central nervous system ria the sensory nerves. If, e.r/., in a dog 

 breathing normally, the central end of the sciatic is rhythmically 

 excited with weak induced currents of varying frequency (40-80 

 per minute), it will be seen after a longer or shorter latent period 



