Action of Carbon Dioxide and Adrenalin on the Heart. 381 



administration of C0 2 and adrenalin the ventricle drops to half its previous 

 rate, due to heart block. 



Volume Changes in the Heart. — During the administration of CO2 the 

 mean volume of the heart is shifted towards the diastolic side, while adrenalin 

 causes a diminution in the mean volume. This is shown in tig. 2 from curves 

 obtained by the method described in a paper by Fuhner and Starling (12) : 

 the protocols are given below. 



Table V.— Mean Heart Volume. 

 Dog, 164 kgrm. Heart, 128 grm. 



Time. 



Temperature. 



B.P. 



I.V.C. 



Rate 10 sees. 



min. sees. 













35 -5° 



94 



50 



20 



1 30 





88 

 86 



65 



1 11 per cent, CO*. 



1 





. 75 



1 





96 



55 



21 



1 





92 



48 



23 



2 c.c. adrenalin, 



1 /100000. 









1 . 





94 



42 



35 



During the administration of 11 per cent. CO2, this heart, weighing 128 grm., 

 increased 50 c.c. in capacity. 



Fig. 3 is taken from an experiment in which the cardiac volume was 

 recorded by a plethysmograph attached to an Albrecht piston recorder of 

 brass with vulcanite piston. It shows that the systolic volume is first 

 increased, followed by increase in the diastolic volume during the same beat, 

 the excursion being the same as before. The heart does not contract to its 

 previous volume, but takes a new increased length. It may come to an 

 equilibrium in the position of increased mean cardiac volume : but usually 

 in our experiments the course shown in the figure is taken and the heart 

 continues to dilate ; the excursions become smaller as the systolic volume 

 increases more rapidly than the diastolic volume, so that the output per beat 

 is diminished and may even cease. The dilatation is greater, the larger the 

 amount of CO2 in the air breathed. When the C0 2 is removed and air 

 respired, the heart resumes its normal mean volume gradually, and as the 

 systolic volume now decreases more rapidly than the diastolic volume, the 

 excursion of the recording lever (output per beat) is increased, and may for a 

 time be above normal. 



When 1 c.c. of a 1 in 10,000 solution of adrenalin was added to the blood 

 in the experiment (Table V), bringing the concentration in the circulating 



