222 PHYSIOLOGY CHAP. 



organ in man and in intact animals. It consists in a rhythmical 

 elevation of the intercostal spaces corresponding with the peri- 

 cardial region to the left of the sternum. The impact is generally 

 supposed to be greatest at the level of the fifth intercostal space, a 

 little within the mamillary line, where the apex of the heart lies 

 normally ; but from a series of careful investigations by Mariannini 

 and Narnias (1882) it appears, on the contrary, that the point 

 at which the beat of the heart is normally strongest corresponds 

 more frequently (in 67 per cent) with the fourth than with the 

 fifth intercostal space, in the supine horizontal position. It is 

 usually perceived by palpation, but in thin persons with large 

 intercostal spaces it is visible to the eye. 



Harvey was the first to point out that the cardiac beat 

 occurred during systole. His theory is the more valuable, inas- 

 much as he had the opportunity of directly observing the beats of 

 the heart on Viscount Montgomery, who had lost part . of his 

 thoracic wall through an accident, so that the exposed heart was 

 visible (Exercitatio de generatione animalium, lii.). 



This generally accepted doctrine, which has received ample 

 confirmation from modern researches with the graphic method, was 

 at one time contradicted, on the strength of fallacious observations 

 in which the ictus cordis was regarded as the effect of the sudden 

 dilatation of the ventricles at the moment of presystole. Corrigan, 

 Stokes, Pigeaux, Burdach (1832), Beau (1835), Baccelli (1859), 

 successively held a brief for this theory, which owed its success, as 

 Marey remarked, " a ce qu'elle etait simple et logiquement deMuite." 



The first promoters of this theory, Corrigan and Stokes, ad- 

 mitted their error, and that it is still perpetuated by the Italian 

 clinician Baccelli is doubtless the result of an ambiguity. At the 

 Kome Congress in 1894 he maintained that the impact of the 

 heart coincides with the moment immediately preceding systole. 

 It is obvious that by systole he means the period of evacuation or 

 ventricular efflux, as was always understood by physiologists as 

 well as clinicians, prior to the introduction of the graphic method. 

 But since it is now well established that the efflux is preceded by 

 a period of tension or of latent systole, which lasts from 0*10 to 0*08", 

 it is clear that this must be the moment with which, according to 

 Baccelli, the impact of the heart coincides. We are completely at 

 one with this opinion, provided it be understood in the sense that 

 the displacement of the thoracic wall reaches its greatest height 

 during that period. It agrees, in fact, perfectly with what we 

 learn from the cardiogram. 



The method now generally adopted by physiologist*) and clinicians in 

 recording the tracings of the cardiac beat (cardiogram) is that of tambours 

 with an elastic membrane and air transmission. Hiirthle, in 1892, made an 

 interesting control research with the different models of cardiographs as 

 employed by various workers. This was the more useful since we should, 



