67 
If one were to use these figures to decide, the indication would he 
that the natural 1- and synthetic dl- products have an equal mydriatic 
action. 
As is shown in a study of large numbers of eyes a 1 : 2,000 solution 
ma}^ in certain cases bring about maximum dilation in as short a 
time as a 1:1,000 solution, and in rare instances a 1:5,000 solution 
may compare veiy favorabh’- with a 1 : 1,000 solution, and thus throw 
more or less doubt upon such determinations as agree with results 
obtained by the blood-pressure method. This criticism holds for 
eyes of different frogs; but it does not hold when comparing a 1 : 1,000 
solution with a 1 :5,000 solution upon the right eye and left eye of 
the same frog. In this case a series of experiments will quickly 
determine which is the stronger of the two solutions, and b}^ proper 
checking against a solution of known strength the approximate 
strength of the unknown can be determined. All later experiments 
with the pupil indicate that the relative activity for natural 1- and 
s}uithetic dl- adrenalin is about the same as determined by blood- 
pressure experiments. In experiment 75 the right eye was placed 
in a 1:40,000 solution of natural 1- adrenalin, the left in a 1:40,000 
solution of s}mthetic dl- adrenalin. The former dilated to a maxi- 
mum in tweiit^^-seven minutes; the latter in forty-six minutes. 
The pupils were then placed in several changes of fresh Ringer, 
whereupon they gradually constricted. Upon placing them again 
in fresh 1:40,000 solutions the right e^^e dilated in the natural 1- in 
sixt^-eight minutes and the left eye in sjmthetic dl- in eighty minutes. 
This and similar experiments now in progress illustrate in a general 
wa}' the relative mydriatic action of these two compounds much 
more truly than is illustrated in a summary of 1113^ older experiments. 
In conclusion it ma}' be said that a method for the standardizing 
of adrenalin preparations which involves the idea of minimum 
doses is unreliable. The pupil method is no exception to this rule, 
for minimum doses are even more uncertain in their action upon the 
frog’s e3"e than the3^ are in blood-pressure experiments. It may be 
assumed that adrenalin acts upon muscle much as does a tetanic 
stimulus, in which case to secure -comparative results upon a given 
muscle the stimulus, preferabl}^ an optimal one, must be of like 
intensit}^ and duration. In aiij case the pupil reacts at different 
rates with different concentration of adrenalin. And the time 
required for dilation seems to be a better index to the strength of 
chemical stimulus than the amount of dilation. When the time inter- 
vening between the moment of stimulation and that of maximum 
dilation is chosen as the unit results ma}^ be obtained that compare 
veiy favorably with those obtained in blood-pressure experiments. 
The S3uithetic dl- adrenalin has about the same activit}’^ as is indicated 
hy the blood-pressure and toxicit}^ experiments alread}^ discussed. 
