ACTION ON THE HEART AND VAGUS IN FrtOGS. 207 



^.ures, irritation of the venous sinus causes cessation of the 

 beats ; but during stillstand from cold, each irritation of it 

 produces a single contraction, and during stillstand from heat 

 produces tetanus of the heart. The inhibitory centres through 

 which the irritation of the sinus acts, at ordinary temperatures 

 in producing slowing and stoppage of the heart, seem there- 

 fore to be completely paralysed by heat, as otherwise they 

 would prevent the contraction from becoming tetanic, and 

 would only allow it to be intermittent. 



Schelske also found that if the vagus, which usually causes 

 slowing, be irritated by a strong electric current, while the 

 heart is in this condition of stillstand from heat, an undulating 

 contraction is produced. 



This may be due, as Cyon thinks, to the current being partly 

 conducted to the heart, and irritating it directly ; but it seems 

 to strengthen the supposition that the inhil)itory centres in 

 the heart, and through which the vagus usually produces slow- 

 ing, are paralysed. 



rickford. Budge, Tigger, and Panum found that the hearts 

 which were exposed to a high temperature soon ceased beatins" 

 and lost their irritability, so that they no longer contracted on the 

 application of a stimulus either mechanical or electrical, while 

 those exposed to a moderate temperature continued to beat, and 

 retained their irritability for a very much longer time. 



Budge and Tigger had assumed that the action of tempera- 

 ture on the mammalian heart was the same as on that of the 

 frog ; but as Nysten had not noticed temperature to exert any 

 particular influence over the time that the mammalian heart 

 retained its irritability after separation from the body, while its 

 action was so marked in frogs, Panum thought it well to test 

 this assumption by experiment. 



He took three rabbits of exactly the same age, and as nearly 

 as possible of the same size and strength, killed them by divid- 

 ing the spinal cord in the neck, and at once removed the heart 

 and lungs. These were then placed in vessels in which the air 

 was kept moist so as to prevent the irritability of the heart 

 being injured by drying. The temperature in one vessel was 

 42-8° P., in a second 61-7° P., and in the third 91-4^ P. The 



