I. One of the methods most widely used of estimating the efficacy of digitalis leaf and the drugs prêpared from it is Focke's frog method, which surpasses all others in accuracy. But as the rate of absorption of the drug under investigation differs remarkably according to individual animals, and also the sensibility of animals varies widely in different seasons, the value obtained by this method may sometimes not be coincident for the drug of the same efficacy. Now if an excised auricle of a frog's heart is kept alive in Ringer's solution at 25°C., to which a given quantity of the drug is added, whose pharmacological efficacy is to be investigated, and the time needed to cause the standstill of the auricle is observed, next the quantity of strophanthin which is needed to bring the standstill in the same length of time is determined, this quantity expresses the value of the pharmacological efficacy of the drug. By this method, we can eliminate errors due to the individual difference in the rate of absorption and the sensibility of the animals and determine the value very accurately. Using this method the following data have been obtained.
II. The pharmacological efficacy of digitalis leaf varies under different conditions:
(1) It differs according to the species of digitalis. Digitalis purpurea is much more effcient than digitalis alba and digitalis campanulata. Digitalis purpurea has been the material used in my present investigations, since it is the digitalis indicated in the pharmacopoeia japonica.
(2) The efficacy of digitalis differs greatly according to the part of the plant. Buds and petals are the strongest. The leaf is next and the stem and the root are the weakest. The efficacy of the leaf differs again according to the position. The middle leaf is most efficacious, the upper and the basal leaves give a far less efficacy, not more than half of that of the former.
(3) As to the relation of the efficacy to the years of growth, the third year herb is the strongest, and the second, the fourth and the fifth year herbs are much weaker and their efficacy is about half of the third year herb.
(4) As to the seasonal difference of the pharmacological efficacy of the third year herb, the efficacy is greatest in May or before the flowering season. After the fall of the flowers or in July, the effectiveness makes a sudden decrease, being about one fifty of that in May. After that, it gradually increases until January, at which time it becomes about equal to that in May.
(5) The efficacy before the flowering season differs according to the kinds of manure. Generally vegetable and animal manures augment the efficacy, while mineral manure tends to lessen it. But there is no definite relation between the strength of the efficacy and the state of growth.
(6) The efficacy varies very widely in the different places in which the herb is cultivated; the strongest is about 5 times more efficacious than the weakest.
III. The method of preservation greatly influences the pharmacological efficacy.
(1) The method of desiccation for preserving the leaves changes the efficacy differently. Leaves which are dried in direct sunshine have the greatest efficacy; next efficacious are those which are desiccated in the shade and in the vacuum-sulphuric acid exsiccator. Those which are desiccated in 100°C., 75°C. and 50°C. are the weakest, their efficacy being only half that of those desiccated in the direct sunshine.
(2) The dried leaves when preserved in a vessel which is air-tight undergo a gradual decrease of the efficacy, the rate of which is very small, only decrease of 5% in one year being observed.
(3) The digitalis leaf sold in the market differs in the content of water and consequently in its efficacy at the time of unsealing. That which has less water content has greater efficacy, and that which has more is weaker in efficacy.
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