666 
PROFESSOR H. N. MARTIN ON THE INFLUENCE OF VARIATIONS 
governance of nerve centres located outside it in the body, would, if isolated, respond 
in like manner to similar temperature changes. 
While experiment upon the isolated hearts of Frogs, Fishes, and Bird embryos, 
combined with the changes in the pulse-rate observed when Mammals are heated or 
cooled, have led to a general consensus of opinion among physiologists that gradual 
and moderate increases of temperature quicken the Mammalian pulse by direct action 
upon the cardiac tissues, and moderate diminutions of temperature similarly slow the 
pulse, the proof that the action of such temperature changes was exerted directly 
upon the heart itself did not seem satisfactory, for the reasons above stated. Hence 
the investigation described in the following pages was undertaken. 
The method. 
The fundamental idea upon which all my work on the isolated Mammalian heart 
has been based is to occlude all vessels of the systemic circulation except those 
supplying the heart itself, while leaving the pulmonary circulation intact. The heart 
and lungs being supplied with blood alone retain their vitality; all extraneous nerve 
centres getting no blood soon die with the remainder of the animal. Moreover, the 
blood supplied to the heart passes through no organ of the body but the lungs, and 
in these it undergoes simple and well understood changes ; no sudden chemical 
alteration in it due to the products of the abnormal activity or commencing death of 
muscle, gland, or brain is possible. As the blood flows around through heart and 
lungs time and again, it no doubt experiences a gradual deterioration due to loss of 
foods and gain of wastes from those organs; but this change is gradual and uniform, 
and if a sufficient quantity of blood be used, the accumulation of wastes (carbon dioxide 
being carried off by the lungs as in normal conditions) and the deterioration in 
nutritive quality do not for some hours alter its constitution- to an extent which in 
any'way interferes with the forcible, regular, and normal beat of the heart. The 
means adopted for renewing the blood circulating through heart and lungs, as also for 
maintaining constant arterial and venous pressures and for regulating the temperature 
of the blood not having as yet been published in detail, and the method also having 
been much modified since the preliminary account was published, it is necessary to 
describe with some minuteness the operation of isolating the heart and the apparatus 
employed for subsequently keeping it alive under approximately normal and readily 
controllable conditions. I do this the more readily as the present form of the 
apparatus is the result of more than a year’s experience and the accumulated 
improvements suggested by several workers (among whom special acknowledgment 
is due to my friends and pupils W. H. Howell and F. Donaldson), so that it now 
leaves little to be desired in the convenience with which it admits of keeping a heart 
under conditions in which venous pressure, arterial pressure, and temperature are readily 
ascertained and controlled. So far as the present series of experiments (those relating 
