1883.} Physiology. 217 
bundle with the cardio-inhibitory branches, their action is, in or- 
dinary cases of stimulation, obscured by that of the latter. All 
physiological analogy suggests the existence of nerve fibers of 
similar function in the higher animals. 
Gaskell (Journ. Physiology Vol. 111, Nos. 5 and 6), has gone 
farther than this, and shown that. stimulation of the pneumo- 
gastric causes, under certain conditions, strengthening, instead of 
weakening, of the heart-beat without alteration of its rhythm; 
and in the tortoise he has actually dissected out a nerve twig, run- 
ning over the surface of the heart, the stimulation of which causes 
simple strengthening of the heart-beat uncomplicated by any other 
modification. 
It is, then, to-day clear that all the variations of force and fre- 
quency of action to which we know the heart-beat is subject, may 
be brought about by the excitement of certain nervous centers in 
the brain; and as nature is not in the habit of letting her powers 
lie idle, it is pretty certain that nervous impulses with the four 
distinct missions that have been indicated do, in the living body, 
descend from the brain to modify the action of the heart. 
In the living animal the arteries are overfull, and the elastic 
arterial wall straining upon the blood inclosed by it, forces the 
fluid with a definite pressure onward on its path of circulation. It 
is this pressure of the blood in the aorta which the heart must 
Overcome in emptying its ventricles ; and it is a question of fun- 
damental physiological importance whether in the mammal varia- 
tions in arterial pressure, that is the resistance which the heart has 
to overcome, cause corresponding variations in the pulse rate. 
This problem, whose solution is apparently so simple, has been 
answered in every possible way by different and equally compe- 
tent experimenters. With the heart in the body, and in physio- 
‘ogical connection with the vascular apparatus, the conditions of 
experimentation are hopelessly complicated. 
qi little more than a year ago, Professor Martin at Baltimore 
_ (Studies Biol. Lab. Johns Hopkins Univ. Vol. 11, No. 1), hit upon 
an ingenious and simple method of isolating completely the living 
‘Mammalian heart from the rest of the body. Martin’s method con- 
_ -Sists, essentially, in opening the chest of a completely narcotized 
_ Gg; all the arteries arising near the heart are tied, except two ; 
_ one of these is connected with a mercury manometer, by means of 
: ` which the amount of blood pressure and the pulse rate are re- 
_ Corded; the other open artery has inserted in it a tube through 
| Which blood may flow from the heart. All the great veins enter- 
: “me the heart are tied, except one, and into this is allowed to flow 
: ‘Wake defibrinated blood from a flask. When the proper temperature 
: Pe site respiration are maintained, the heart may continue to 
vad S 
normally for hours, On the heart thus severed from its 
a 
_ P’¥siological connection with every other organ, a most import- 
: NaON, interesting series of studies has been made by Professor 
