24 
time the leaves show the effect by a lessened toxicity, the relation 
being reversed, as at this time the first-year leaves are stronger. 
The effect of daylight was found to be very slight, even if the leaves 
were exposed to its influence for a year. As to the effect of the 
aging of the leaves he found that if they were collected and dried in 
the air in the ordinary way and preserved in non air tight flasks 
they will lose a large part of their activity. 
The greatest factor in this deterioration Focke considers to be the 
moisture content, and the changes which the leaves undergo during 
the first few months after their collection are largely due to this, as 
in the presence of moisture certain ferments present in the leaves 
are able to destroy some of the active constituents. To avoid this, . 
he heats the leaves rapidly and strongly at a temperature not over 
100° C., and when they are dried so as to contain only about 1§ per 
cent moisture they are preserved in lots of 50 grams in dark, air- 
tight jars. He found that if dried and preserved in this manner 
they lost only 5 per cent in V in a year. The last. 1 per cent of mois- 
ture left in the leaves seemed to be bound in sonin manner, so that 
it was not active.® To show the importance of the moisture content 
factor, Focke believed that only about one-fifth of the differences in 
strength were due to all the other factors. 
To avoid the variation due to the different localities, the leaves 
from all the different sources should be powdered after drying and 
mixed, so as to give a uniform product. 
Siebert b reports the efforts of himself and Ziegenbein to determine 
a method by which digitalis and strophanthus preparations could be 
standardized biologically. The method adopted by them was the 
one developed by Arthur and Hans Meyer, which has been described 
earlier in the discussion of Ziegenbein’s work. 
In fifty experiments with digitalis leaves the most active preparation 
showed a toxicity of 0.03 gram for 100 grams frog weight, while the 
weakest required 0.075 gram to produce death. They, therefore, 
adopted as a standard strength for digitalis leaves 0.04 gram for 100 
grams frogs. 
The variation in strophanthus preparations was as follows : Weakest 
0.06, strongest 0.008 c.c. for 100 grams frogs. The standard they 
adopted was 0.02 c.c. 
An important chapter on the subject relating to the comparative 
study of the chemical and biological methods of assay of digitalis 
a In this connection it is interesting to note that in 1867 Tourdes (Gaz. med. de 
Strasb., 1867, XXVII, 191) pointed out that the reason the digitalis preparations 
obtained in Strassburg were superior to those used elsewhere was because the leaves 
of the second year's growth were employed after having been selected carefully and 
dried first in the shade, and then in an oven at a temperature not over 40° C. The 
leaves were then preserved in tin or glass vessels away from the light and moisture. 
b Siebert, Berl. klin. Wchnschr., 1903, XL, 813. 
