Volume 1

A text-book of human physiology : including histology and microscopical anatomy with special reference to the requirements of practical medicine / by L. Landois ; translated from the seventh German edition with additions by William Stirling.

Landois, L. (Leonard), 1837-1902. Lehrbuch der Physiologie des Menschen. English

Date:: 1891

Credit: A text-book of human physiology : including histology and microscopical anatomy with special reference to the requirements of practical medicine / by L. Landois ; translated from the seventh German edition with additions by William Stirling. Source: Wellcome Collection.

136/602 page 96

$proved that the heart-apex is devoid of all nervous structures, which may act as originators of these rhythmical impulses.] ^ c a rAction of Drugs.—If the heart-apex contains no nervous structures, it must form a good ob ect for the study of the action of drugs on the cardiac muscle Some of these have bßen J ' 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 alkah and vice versa. Digitalin, antiarin, barium, and veratria act like alkalies, while saponin, muscarin, and Pilocarpin have the ettect of acids (§ 65). An isolated frog's heart, fatigued after being supplied with a solution of blood, is caused to beat more vigorously 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 application of normal saline solution (O'G per cent. NaCl), while its activity may be restored by supplying it with albuminous and other fluids (p. 92).]. II. Direct Stimulation of the Heart. AH direct cardiac stimuli act more energetically on the inner than on the Yicf, 72. outer surface of the heart. If strong ° * ^i..,-,i„p stimuli are applied for too long a time, ^^^'^ 'S^^l^l^i:^ the ventricle is the part first paralysed. (.) Thermal ~Ä«ff^ aÄt7e ^nd ^!L%SSS of Z ÄT Derca^te (1644)' otZTeTtt t.ft^^^^^^^ the number of pulsations of an eel's heart.] Descartes ^io^*; ^^^^^ ^^^^ temperature increases, the number of beats is at first considerably increased, but afterwards the beats again become fewer and if the temperature is raised above a certain Uinit tUe heart'stands still, the myosin of which its fibres consist is coagu- lated, 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 (SchelsJce). The size and extent of the contractions increase up to about 20° C, but above this point they diminish (fig. 74). The ^mc occupied by any «i^gle con- traction at 20° C. is only about ^^th of the time occupied by a contraction occurring at 5° C. A heart which has been warmed is capable of reacting pretty rapidly to intermittent stimuli while a heart at a low temperature reacts only to stimuli occurring at a considerable interval (G^awie). • j- • • -u j Cold.—When the temperature of the blood is diminished, the ^ \^ heart beats more slowly. A I frog's heart, placed between two watch-glasses and laid on ice, beats very much more slowly. The pulsations of a frog's heart stop when the heart is exposed to a temperature of 4° C. to 0°. If a frog's heart be taken out of warm water, and suddenly placed upon ice, it beats more rapidly, and Fig. 73. Roy's heart tonometer, h, heart; o, air-tight chamber p. piston ; I, writing-lever ; e, outflow tube, conversely, if it be taken from ice and placed over warm wat^r, it beats more slowly at first ^^MXi^^iKrot^^^^^^$