676 
PROFESSOR H. N. MARTIN ON THE INFLUENCE OF VARIATIONS 
this quantity it was possible to obtain from Dogs. When four litres or more of blood 
are wanted it becomes practically impossible to use Dog’s blood, and so some other 
had to be selected. After several trials Calf’s blood was chosen. This blood, how¬ 
ever, nourishes the heart less satisfactorily, and hence the earlier indications of 
commencing death. 
With respect to the choice of blood I add a few words which may be of aid to any 
one desirous to repeat my experiments. It is important to have it from quite young 
Calves ; that is to say, from animals which are still suckling : a point of itself of some 
interest when considered in connexion with the well known fact that the chemical 
composition of the urine of the nurslings of Herbivora shows that their nutritional 
processes agree in the main with those of adult Carnivora, and differ essentially from 
those of the adults of their own species. In spite of all care I used to be frequently 
disappointed by the death of the isolated heart before any satisfactory number of 
observations could be carried out upon it, even in cases when I could think of no 
cause for the failure. Light broke upon me when the laboratory attendant, whose 
duty it was to bring the blood from the' slaughter-house, remarked one day that it 
seemed to him that we nearly always got on better when he did not get the blood 
from “wharf calves.” On questioning, I found that “ wharf calves ” was the term 
employed by Baltimore butchers to indicate animals which, though still young enough 
to yield veal, were of such age that they had long ceased to live on milk. Since the 
blood of such Calves has been rejected the percentage of failures has considerably 
decreased. It is hardly necessary to add that care must be taken that no extraneous 
matter enters the blood during its collection. Baltimore butchers stun the Calves and 
then cut their throats, and while the blood flows out vomiting frequently occurs 
and sends the contents of the stomach into the collecting pail. The blood from each 
animal has therefore to be collected separately, so that the quantity already obtained 
may not be rendered unfit for use by admixture with matters from the stomach of 
another animal. 
Even with the best obtainable Calf’s blood, however, the results are not as satis¬ 
factory as with Dog’s blood. Not only does the heart die sooner, but other changes 
occur which shorten the time during which an experiment can be carried on. The 
most marked of these is lung oedema, which nearly always takes place in the course of 
an hour and a half, to such an extent as to seriously impede the pulmonary circulation 
and the aeration of the blood in the lungs. In consequence, the supply of blood to the 
left heart is hindered, and the right heart becomes gorged, and its auricle finally 
paralyzed ; and this, of course, puts an end to an experiment. Another trouble which 
is apt to occur when Calf’s blood is used is considerable pericardial exudation, often to 
such an extent as to seriously interfere with the beat of the heart. This difficulty 
may, however, be readily avoided by cutting a small hole in tire pericardium as soon 
as the heart is placed in the warm chamber. A third difficulty met with when Calf’s 
blood is employed is more serious. Many observers have noted on the isolated Frogs 
