380 PSYCHOLOGY. 



thrown on the eyes, 28 for green, 30 for yellow, 35 for orange, 

 and 42 for red. Red is thus the most exciting color. 

 Among tastes, sweet has the lowest value, next comes salt, 

 then bitter, and finally sour, though, as M. Fere remarks, 

 such a sour as acetic acid excites the nerves of pain and 

 smell as well as of taste. The stimulating effects of tobacco- 

 smoke, alcohol, beef-extract (which is innutritions), etc., etc., 

 may be partly due to a dynamogenic action of this sort. — 

 Of odors, that of musk seems to have a peculiar dynamo- 

 genic power. Fig. 85 is a copy of one of M. Fere's dyna- 

 mographic tracings, which explains itself. The smaller 

 contractions are those without stimulus ; the stronger ones 

 are due to the influence of red rays of light. 



Fig. 85. 



Everyone is familiar with the patellar reflex, or jerk up- 

 wards of the foot, which is produced by smartly tapping 

 the tendon below the knee-pan when the leg hangs over 

 the other knee. Drs. Weir Mitchell and Lombard have 

 found that when other sensations come in simultaneously 

 with the tap, the jerk is increased.* Heat, cold, pricking, 

 itching, or faradic stimulation of the skin, sometimes strong 

 optical impressions, music, all have this dynamogenic effect, 

 which also results whenever voluntary movements are set 

 up in other parts of the body, simultaneously with the 

 tap.t 



These ' dynamogenic ' effects, in which one stimulation 



♦Mitchell in (Philadelphia) Medical News (Feb. 13 and 20, 1886); Lom- 

 'bard in American Journal of Psychology (Oct. 1887). 



f Prof. H. P. Bowditch has made the interesting discovery that if the 

 reinforcing movement be as much as 0.4 of a second late, the reinforce- 

 ment fails to occur, and is transformed into a positive inhibition of the 

 knee-jerk for retardations of between 0.4' and 1.7'. The knee-jerk fails 

 to be modified at all by voluntary movements made later than 1.7' after 

 the patellar ligament is tapped (see Boston Med. and Surg. Journ., May 31, 

 1888). 



