1893.] On the Physiology of the Embryonic Heart 463- 



administered, and in two minutes the rhythm rose to 100 per minute, 

 and remained constant for two and a half minutes, when it fell to 96 

 per minute. A second dose of 0' 0001 5 gram raised the rate to 102 

 per minute. The beats were also of greater force, since more blood 

 was seen passing through the heart. A dose of 0*0025 gram was 

 fatal. When given to an embryo, aged seventy-five hours, at 37 C., 

 beating with a rhythm of 116 per minute, it reduced the rhythm, 

 after one minute's action, to 100 per minute. The beats, however, 

 remained very strong. After one minute forty-five seconds' action 

 the heart stopped in strong systole, but started again and gave a few 

 powerful beats. After the drug had acted nine minutes thirty seconds 

 the heart stopped permanently in powerful contraction. Caffeine, 

 therefore, acts directly on the cells of the embryonic heart. 



b. Strychnine was given to a seventy hours' embryo in a dose of 

 0-000017 gram, and depressed the rhythm of the heart from 112 per 

 minute to 52 per minute. There was no spasm. In an eighty hour 

 embryo, at 39 C., a dose of 0'00002 gram temporarily increased the 

 rhythm, both in force and number of beats ; then the systole rapidly 

 became weakened and the rhythm irregular. A further dose of 

 0'00002 gram still more rapidly reduced both force and frequency of 

 beating, till death in diastole occurred. 



c. Morphine acetate, if given in doses of O'OOOl gram, is a powerful 

 depressant. With a dose of 0'0002 gram, after one minute's action 

 on an eighty-five hours' embryo at 40 C., irregularities and slowing 

 were obtained ; after two minutes' action the beating stopped, but 

 went on again, the waves of contraction sometimes passing from 

 ventricle to auricle, and at others in the normal direction. Periods 

 of rest alternated with violent bouts of rapid beating. 



d. Veratrine. Doses of O'OOOl gram increase the number of beats 

 per minute. Larger doses may cause, temporarily, an increase of 

 rhythm, but soon depress the heart by greatly lengthening the 

 systole, which becomes very weak while the diastole is complete. 

 The heart stops in an expanded condition. The heart of a seventy-two 

 hours' embryo that had stopped in diastole, after a dose of 0'0005 gram, 

 was restored by the application of O'Ol gram of potassium chloride 

 almost to its normal rhythm. This agrees with Ringer's observation 

 on the frog's heart. 



e. Potassium chloride, when applied in a dose of 0'005 gram to an 

 embryo aged seventy-two hours, reduced the normal rhythm of 76 

 per minute to 60 per minute. A further dose of O'Ol gram reduced 

 the rhythm to 64 per minute. After the administration of a total 

 amount of 0'07 gram of the substance, the heart stopped in 

 diastole. 



f . Nicotine, in very minute doses, stimulated the embryonic heart ; 

 J c.c. of a solution containing f c.c. of nicotine to 100 c.c. of normal 



