to an action upon the heart but upon the medulla. In every animal we 
examined we found the heart beating after the respiration had stopped, 
and it continued to beat as long as artificial respiration was maintained. 
It would not then be at all surprising if two solutions which showed 
a certain relationship when the cardiac action was concerned should 
show an entirely different relation when the central nervous system 
was the point of attack. One solution might be very weak in its 
action upon the heart and yet contain decomposition products of 
digitalis whose typical action is upon the medulla and it would 
therefore appear unduly strong when judged by such a standard. 
For this reason we think that methods which employ as a standard, the 
minimum lethal dose obtained upon the higher animals are not applicable 
to the physiological assay of the digitalis series. 
It is possible that still further complications would arise in using 
such methods in that on certain animals of the same species some 
would die from the cardiac effect and others from the medullary 
action. In some of the cats, for instance, distinct respiratory move- 
ments were seen after the heart had stopped and the blood pressure 
had fallen to zero; in others the respiration stopped first. As stated 
earlier, to avoid complications of this sort, in our experiments on cats 
we always employed artificial respiration. 
Comparing the toxic doses obtained upon cats and frogs (twelve- 
hour method) we have in both cases a cardiac action and three of the 
four preparations show relatively the same activity; the Parke. Davis 
& Co. Fluid Extract alone being an exception. But that an exception 
should occur is not to be wondered at when the differences between 
the heart of the frog and that of the cat are considered. Also in the 
blood pressure experiments on the cat we have to do with substances 
acting upon the vessel walls as well as upon the heart and this neces- 
sarily introduces another factor as some of the digitalis active prin- 
ciples act more strongly upon vessel walls than others, and in two 
preparations of digitalis the active substances may not be present in 
the same relative amounts. 
The “Focke” and the “one-hour” methods upon frogs might be 
thought to give a closer agreement, but here (aside from the diffi- 
culties connected with Focke’s method which have been discussed) 
we have to deal with the question of ease of absorption. As has been 
pointed out by some earlier writers, in those methods in which the 
time element is very limited, a weak preparation with easily absorb- 
able constituents would appear stronger than a strong preparation 
with constituents which are absorbed with difficulty. It would seem 
that such an objection might be offimportance in the “Focke” method, 
where from seven to twenty minutes only are allowed. As to whether 
it would play a part in the “one-hour” method is of course possible 
