1880.] On the Tonicity of the Heart and Arteries. 



225 



II. "On the Tonicity of the Heart and Arteries." ByW.H. 

 Gaskell, M.D., Trinity College, Cambridge. Communi- 

 cated by Dr. Michael Foster, Prelector of Physiology in 

 Trinity College, Cambridge. Received March 1, 1880. 



The author has made a lengthened series of observations on the 

 heart of the frog and tortoise, both on the entire ventricle and on the 

 apex, supplied, by the help of Roy's* tonometer, with saline solutions 

 or with dilated blood (of rabbit, sheep, or bullock) . 



That the artificial blood solutions differ in their action on the apex 

 from the frog's own blood in degree only and not in kind, and that 

 consequently Bernsteinf is wrong in regarding these fluids as specific 

 stimuli giving rise to rhythmic action, is shown by the following facts. 



1. The apex of the frog's heart brought to quiescence after Bern- 

 stein's method, will beat spontaneously when the pressure in its cavity 

 is increased by clamping the aortic arches. 



2. If Avhile the heart still remains in its natural position within the 

 body, the frog's own blood be replaced by the artificial blood solution, 

 and the ventricle be then nipped by fine forceps, the apex will remain 

 quiescent for an indefinite length of time. As soon, however, as the 

 pressure in the cavity is increased, the apex commences to contract, 

 and beats as long as the heart is distended by the increased pressure. 



The conclusions to which the author has been led by his experiments 

 are as follows : — 



1. The heart possesses, like the arteries, what may be called tonicity, 

 and the variations in this tonicity play an important part in deter- 

 mining the features of the cardiac beat. 



The apex, when first tied on to the cannula, the pressure of the 

 blood solution being kept constant at 10 cm. or less, remains quiescent 

 for some time in the position of greatest relaxation. As, however, the 

 blood solution continues to pass through, the lever of the tonometer 

 rises often very appreciably even before the apex begins to beat. 

 This rise, unless otherwise explained, would seem to show that the 

 first effect of the blood solution has been to bring the apex into a 

 condition which is no longer that *of greatest relaxation for that 

 particular pressure. 



Further, in correspondence with this raising of tone of the cardiac 

 muscle by the artificial blood solution, is the alteration in the character 

 of the beat. 



The first beats, whether natural or artificially produced, which occur 

 while the ventricle is still in a somewhat relaxed or atonic condition in 



* " Journ. of Physiology," vol. i, p. 452. 



f " Centralblatt i. d. Med. Wissenschaften," 1876, p. 385. 



