ACTION OF HEAT AND DEUGS ON THE HEART. 



83 



dition of "apparent death," lasting 30-90 mins. ; while, if the action of the fluid be prolonged, 

 the heart may not contract at all , even when it is stimulated electrically or mechanically. It 

 may be made, however, to pulsate again, if it be supplied with saline solution containing blood 

 (1 to 10 per cent). If the ventricle be nipped with wire forceps at the junction of the upper 

 with its middle third, so as to separate the lower two-thirds of the ventricle, physiologically but 

 not anatomically, from the rest of the heart, then the apex will cease to contract, although it is 

 still supplied with the frog's own blood {Bernstein, Bowditch). The physiologically isolated 

 apex may be made to beat by clamping the aortic branches so as to prevent blood passing out 

 of the heart, and thus raising the intracardiac pressure. The rate of the beat of the apex is 

 independent of and slower than that of the rest of the heart. This experiment proves that the 

 amount of pressure within the apex-cavity is an important factor in the causation of the spon- 

 taneous beats of the apex. If blood-serum, to which a trace of delphinin is added, be trans- 

 fused or "perfused" through the heart, it begins to beat within a minute, continues to beat for 

 several seconds, and then stands still in diastole {Bowditch). Quinine and a mixture of atropine 

 and muscarin have a similar action. These experiments show that, provided no nervous appar- 

 atus exists within the heart-apex, the cause of the varying contraction is to be sought for in the 

 musculature of the heart, and that the stimulus necessary for the systole of the heart's apex 

 may arise within itself. If there is no nervous apparatus of any kind present, then we must 

 assume that the heart-muscle may execute rhythmical movements independently of the presence 

 of any nervous mechanism, although it is usually assumed that the ganglia excite the heart- 

 muscle to pulsate rhythmically. It is by no means definitely proved that the heart-apex is 

 devoid of all nervous structures, which may act as originators of these rhythmical impulses.] 



[Action of Drugs. If the heart-apex contains no nervous structures, it must form a good 

 object for the study of the action of drugs on the cardiac muscle. Some of these have been 

 mentioned already. Ringer finds that a calcium salt makes the contractions higher and longer. 

 Dilute acids added to saline solution, e.g., lactic, cause complete relaxation of the cardiac 

 musculature, while dilute alkalies produce an opposite effect or tonic contraction, even though 

 the apex be not pulsating. The action of a dilute acid may be set aside by a dilute alkali and 

 vice versa. Digitalin, antiarin, barium, and veratria act like alkalies, while saponin, muscarin, 

 and pilocarpin have the effect of acids ( 65). An isolated frog's heart, fatigued after being 

 A supplied Avith a solution of blood, is caused to beat more vigor- 



ously by a solution of kreatinin, or extract of meat {Mays).~[ 



[The ' ' heart " preparation in many respects behaves like the 

 foregoing, i.e., it is exhausted after a time by the continued appli- 

 cation of normal saline solution (0*6 per cent. NaCl), while its 

 activity may be restored by supplying it with albuminous and 

 other fluids (p. 79).] 



II. Direct Stimulation of the Heart. All direct 

 cardiac stimuli act more energetically on the inner than 

 on the outer surface of the heart. If strong stimuli are 

 applied for too long a time, the ventricle is the part first 

 paralysed. 



{a) Thermal Stimuli. [Heat affects the member or frequency 

 C 



Fig. 63. 

 A, contractions of a frog's heart at 19 C. ; B, at 34 C. ; C, at 3 C. 



and the amplitude of the pulsations, as well as the duration of the systole and diastole and 

 the excitability of the heart.] Descartes (1644) observed that heat increases the number of 

 pulsations of an eel's heart. As the temperature increases, the number of beats is at first con- 

 siderably increased, but afterwards the beats again become fewer, and if the temperature is 

 raised above a certain limit the heart stands still, the myosin of which its fibres consist is 

 coagulated, and "heat-rigor" occurs. Even before this stage is reached, however, the heart 

 may stand still, the muscular fibres appearing to remain contracted. The ventricles usually 

 cease to beat before the auricles {Schelske). The size and extent of the contractions increase up 

 to about 20 C, but above this point they diminish (fig. 63). The time occupied by any single 



