BIOCHEMISTRY: MACHT, HERMAN AND LEVY 
583 
In complete agreement with the localization of pain points on the 
surface of the body, as described by v. Frey,^ and others, we have found 
that at any given spot of the body a definite pain sensation can be 
eHcited by changes in mutual inductance of sufficient intensity, and that 
for every group of pain points a pain sensation of exactly the same 
quality and intensity can be elicited by exactly the same intensity of 
electrical stimulus. By practice we were able to distinguish changes in 
pain sensation produced by moving the secondary towards or away 
from the primary coil a distance of not more than 0.1 cm. 
Through numerous observations it was estabHshed that the normal 
pain threshold remains surprisingly constant for many hours in succes- 
sion, and, through a series of other experiments, lasting over 25 hours 
each, the diurnal and nocturnal variations were found to be very slight. 
Having determined the normal pain threshold in any given experi- 
ment, a drug was administered by subcutaneous or intramuscular in- 
jection, and, after its absorption, repeated readings were made. In 
this way a rise or fall in the pain threshold, or an analgesic or hyper- 
algesic effect respectively, was detected and measured. The experi- 
ments were performed on Dr. Macht and two medical students, Messrs. 
N. B. Herman and C. S. Levy. 
Being fully aware of the fact that certain subjective elements, in- 
herent in the character of the investigation, enter into our experi- 
ments, we have taken all possible precautions to eliminate errors aris- 
ing from this source, and have made numerous control experiments. 
Each experiment was carried out in the same room, and under per- 
fectly constant conditions. Readings were always taken with the sub- 
ject in the same position, and the subject was never allowed to look at 
the apparatus, but sat either with eyes closed or fixed on some distant 
point. The electrodes employed were of course the same in any one 
experiment; the distance, between the electrodes was kept fixed; the 
pressure with which they were applied to the surfaces was kept constant; 
the direction of their application was the same; and the wetness of the 
surfaces stimulated was maintained the same as nearly as could be 
judged. 
When a drug was administered, the subject was ignorant of its 
nature. Furthermore, as controls, normal saline and other inactive 
substances were often substituted in place of the drug without the sub- 
ject's knowledge. It may be remarked in passing, that owing to the 
conflicting experiences of previous observers, we could not know the 
true pharmacological action of most of the alkaloids studied; thus 
further eliminating any subjective bias. 
