THE CIRCULATION OF THE BLOOD. 263 
ture, or otherwise, either together or singly, continue to beat, 
whether amply provided with or surrounded by blood. 
3. The ventricle thus separated displays less tendency to 
beat independent of some stimulus (as feeding under pressure), 
though a very weak one usually suffices—i.e., its tendency to 
spontaneous rhythm is less marked than is the case with the 
other parts of the heart. These remarks apply to the hearts 
of Chelonians—fishes, snakes, and some other cold - blooded 
animals. 
4, In certain fishes (skate, ray, shark) the beat may be re- 
versed by stimulation, as a prick of the ventricle. This is 
accomplished with more difficulty in other cold-blooded animals, 
and still more so in the mammal. 
5. In certain invertebrates, notably the Poulpe (Octopus), a 
careful search has revealed no nerve-cells, yet their hearts con- 
tinue to beat when their nerves are severed, on section of 
parts of the organ, etc. 
6. A strip of the muscle from the ventricle of the tortoise, 
when placed in a moist chamber and a current of electricity 
passed through it for some hours, will commence to pulsate and 
continue to do so after the current has been withdrawn; and 
this holds when the strip is wholly free from nerve-cells. 
From the above facts certain inferences have been drawn: 
1. It has been concluded that the sinus is the originator and 
director of the movements of the rest of the heart. 2. That this 
is owing to the ganglia in its walls. While all recognize the 
importance of the sinus, some physiologists hold to the gangli- 
onic influence as essential to the heart-beart, still ; while others, 
influenced by the facts mentioned above, are disposed to regard 
them as of very doubtful importance—at all events, as origina- 
tors of the movements of the heart. 
The tendency now seems to be to attach undue importance 
to the spontaneous contractility of the heart-muscle; for it by 
no means follows logically that, because a muscle treated by 
electricity, when cut off from the usual nerve influence that we 
believe is being constantly exerted on the heart like other or- 
gans, will contract and continue to do so in the absence of the 
stimulus, it does so normally; or, because some hearts beat in 
the absence of nerve-cells, that therefore nerve-cells are of no 
account in any case. Such views, when pressed to the extreme, 
lead to as narrow conceptions as those they are intended to re- 
place. 
Taking into account the facts mentioned and others we have 
