42 
strength required 0.42 c. c. As these preparations are both physio- 
logically assayed to a definite strength, the difference must be ascribed 
to the variability of the reaction of the frogs. As a means of demon- 
strating the uniformity of these two preparations mentioned, we might 
say that the 1907 tincture corresponded in strength to a tincture made 
in the laboratory at Ann Arbor from leaves obtained from Parke, Davis 
and Co., while their 1908 preparation is practically the same strength 
as U. S. Pharmacopoeia fluid extracts made by other firms and which 
were examined at the same time, the results being given in the table 
on page 44. 
In striking contrast to these views are the results of some of 
Houghton’s® assays, which were carried out to ascertain if a standard 
tincture would deteriorate in a year if kept under proper conditions. 
His two tables, which we give below, show not only that the standard 
preparations do not deteriorate, but also, what is equally important 
and interesting, that frogs react exactly the same at all times of the 
year. 
Table III A . — Standard strophanthus. 
Date. 
Toxic dose. 
July 6, 1897 
October 19, 1897 
December 20, 1897 
February 23, 1898 
April 25, 1898 
0. 00015 
. 00015+ 
. 00015 
. 00015- 
. 00015 
Table III B. — Concentrated strophanthus. 
Date. 
Toxic dose. 
July 28, 1897 
November 10, 1897 
0. 0000037 
. 0000037 
Ziegenbein also did not think that season made much difference in 
the susceptibility of frogs. However, it may be said that any errors 
due to differences in the reaction of the frogs dependable upon 
season can be avoided, in the first place, by standardizing the frogs 
with reference to the temperature of the operating room after the 
manner of Focke, and, second and more simply, these differences may 
be avoided by always assaying a standard solution of digitalis, which 
is kept under proper conditions at the same time that the unknown 
solution is examined. 
FROG-HEART METHODS OF ASSAY. 
According to our classification, the second group is concerned with 
an action upon the frog’s heart as a means of measuring the compara- 
tive strengths of the different preparations. In these methods the 
a Houghton, J. Am. Med. Ass., 1898, XXXI, 959. 
