ANIMAL AND VEGETABLE 183 



constantly supplied to the heart,is by way of the sympathetic, 

 while the vagus nerves are inhibitory, or, in other words, 

 exert a governing or opposing electromotive force. They 

 are buffers, or springs, regulating the flow of energy to the 

 heart, much in the same way that a rise or fall of tempera- 

 ture may regulate the fall or rise of a gas-flame in a heating 

 apparatus. 



We learn, from physiological research, that man inhales 

 400 c.c. of oxygen per minute during the daytime and 

 200 c.c. per minute during the night. I know, from my 

 own work, that if the hand-to-hand galvanometric deflec- 

 tion of a normally healthy man during the daytime is 

 350 mm. it will fall at night to about 175 mm. 



That means there is a falling off in the production or 

 reception of nervous energy of fifty per cent. 



But the controlling, governing current from the brain 

 the inhibiting current is also halved, because generation, 

 or reception, is halved, and therefore there is no alteration 

 in equilibrium, and the heart must receive a proportionate 

 supply of energy at all times, supposing there to be no 

 escape of nerve-current or excitement of the vagi. Should 

 such an escape occur, the result, or one result, should be 

 higher blood-pressure, while in the event of anything, such 

 as cold or some toxin, increasing the resistance of the 

 conducting substance of the vagi, the same phenomenon 

 should bepresented,because inhibition would be diminished. 

 On the other hand, any cerebral disturbance tending to 

 unduly stimulate the cardiac branches of the vagi would 

 have the effect of slowing the heart down, possibly in 

 extreme cases to a fatal extent. 



The main differences, so far as I can see, between 

 voluntary and cardiac muscles are : (1) the first are supplied 

 by open circuits through which impulses are sent from the 

 brain ; (2) cardiac muscles form part of a closed circuit 

 or circuits regulated by cell-groups possibly other than 



