TY - JOUR
AB - H. L. Hollingworth,1 professor of psychology at Columbia University, gives a summary of an extended investigation soon to be published in psychologic journals, on the influence of caffein on menial and motor efficiency. The experiments were carried on in a specially equipped laboratory with the aid of six assistants and sixteen subjects, of both sexes, engaged for full-time service extending over a period of forty days. The most rigorous scientific method and precaution were employed throughout the investigation, the full details of which will appear in the complete report. Controls were employed among both the subjects and the assistants. These controls received capsules containing sugar of milk instead of caffein, and no subject knew whether or when he received caffein. The tests performed included motor efficiency measured by steadiness, coordinated movements, typewriting, etc., and mental efficiency measured by speed and accuracy of calculations, discriminations, and other mental processes. The same program of tests was performed for an hour five times each day. A condensed statement of the author's conclusions from 76,000 measurements and 800 efficiency curves with and without caffein follows: In the test for steadiness, in which the arm is held extended and any unsteadiness recorded by appropriate apparatus, doses of from 1 to 4 grains of caffein citrate produced a slight nervousness not apparent until several hours after the dose. A dose of 6 grains produced a marked unsteadiness which was greatest after three or four hours. The effect of caffein on motor processes was that of a typical motor stimulant manifested by a decided increase in the speed and accuracy of the movements. This effect began in from forty-five to ninety minutes and lasted from three to four and one-half hours. No secondary or after-effect was produced in the seventy-two hours during which the effects of single doses were traced. In the coordination tests, of which typewriting is one, caffein citrate in doses of from 1 grain to 3 grains produced stimulation and increase of speed while larger doses produced retardation. In typewriting, however, the quality of the performance measured by the number of errors both corrected and uncorrected, for the whole range of caffein doses, was superior to the quality yielded by the same subjects on control days, and the increase in speed produced by small doses was not gained at the expense of additional errors. In the calculation tests, as well as in other tests of mental processes, all squads showed a pronounced stimulation following caffein. This stimulation amounted to from 10 to 20 per cent. of the initial performance, whereas the control days showed a corresponding decrease of the initial performance due to fatigue. The total effect of caffein was greater for these than for any of the other tests. The stimulation began about one hour after the dose and was still present at the close of the day's work six or seven hours later. No evidence of any secondary depression was found. Instead, the morning following the experiment showed without exception a clear improvement over the work of the morning preceding the experiment. This improvement was not due to practice, as it was never found in the case of the control days. H. C. Wood, Jr.,2 has studied the effects of caffein on the circulatory and muscular systems. The average of all his experiments on the circulation shows a slight increase in blood-pressure beginning one-half hour after the administration of caffein, reaching its maximum in two hours and amounting to an average increase of 2.2 mm. of mercury pressure. The slowing of the pulse-rate began soon after administration of caffein and remained almost constant at an average of five beats per minute slower than before caffein was given. These statements represent averages of experiments made on normal adults under test and control conditions. The doses of caffein citrate ranged from 1½ to 6 grains. Dr. Wood also tested the effects of caffein on the reflexes using the Lombard knee-jerk apparatus. The results he describes as unexpectedly striking. “In every instance there was a marked increase in the knee-jerk beginning about twenty minutes after the ingestion of caffein, reaching its maximum in from forty to sixty minutes, and remaining above normal throughout the whole course of the experiment.” As to the effect on muscular efficiency Wood, after reviewing the results of Hoch’s, Kraepelin's and Shumburg's experiments on the muscular action of human subjects, adds a series of experiments on frog muscles, both caffeinized and normal, and sums up all the evidence with the conclusion that caffein “acts as a stimulant to the reflex centers of the spinal cord; it enables the muscles to contract more vigorously without producing a secondary depression, so that the sum-total of muscular work which can be done by a man under caffein is greater than that which can be done without it.” It is gratifying to have the effects on the human system of a drug like caffein so investigated by rigorous scientific tests at the hands of capable investigators; only in this way will there be provided an adequate basis for correct conclusions as to the possible dangers of the use of caffein-containing beverages. 1. Hollingworth, H. L.: Therap. Gaz., Jan. 15, 1912, p. 1. 2. Wood, H. C.: Therap. Gaz., Jan. 15, 1912, p. 6. JAMA. 1912;58(11):784-785 Back to top Article Information Editor's Note: JAMA 100 Years Ago is transcribed verbatim from articles published a century ago, unless otherwise noted.
TI - THE INFLUENCE OF CAFFEIN ON MENTAL AND MOTOR EFFICIENCY AND ON THE CIRCULATION
JF - JAMA
DO - 10.1001/jama.2012.167
DA - 2012-03-21
UR - https://www.deepdyve.com/lp/american-medical-association/the-influence-of-caffein-on-mental-and-motor-efficiency-and-on-the-er0onZiSf4
SP - 1118
EP - 1118
VL - 307
IS - 11
DP - DeepDyve
ER -