84 rsyriioi.om'. 



oatioTi t(i the motor centre, the sl<iu of certain parts of the body is 

 exposed to <;entle tactile stimulation. ... If, having ascertained the 

 subminimal stnMigth of current and convinced one's self repeatedly of its 

 ineffieacy, we draw our hand a single time lightly over the skin of the 

 paw whose cortical centre is the object of stimulation, we find the cur- 

 rent at once strongly effective. The increase of irritability lasts some 

 seconds before it disappears. Sometimes the effect of a single light 

 stroking of the paw is only sufficient to make the previously ineffectual 

 current produce a very weak contraction. Repeating the tactile stimu- 

 lation will then, as a rule, increase the contraction's extent." * 



We constantly nse tlie summation of stimuli in our 

 practical appeals. If a car-horse balks, tlie final way of 

 starting liim is by applying a number of customary incite- 

 ments at once. If tlie driver uses reins and voice, if one 

 bystander pulls at liis head, another lashes his hind 

 quarters, and the conductor rings the bell, and the dis- 

 mounted passengers shove the car, all at the same moment, 

 his obstinacy generally yields, and he goes on his way re- 

 joicing. If we are striving to remember a lost name or fact, 

 we think of as many ' cues ' as possible, so that by their 

 joint action they may recall what no one of them can recall 

 alone. The sight of a dead prey will often not stimulate a 

 beast to pursuit, but if the sight of movement be added to 

 that of form, pursuit occurs. " Briicke noted that his brain- 

 less hen, which made no attempt to peck at the grain under 

 her very eyes, began pecking if the grain were thrown on 

 the ground with force, so as to produce a rattling sound." t 

 " Dr. Allen Thomson hatched out some chickens on a carpet, 

 where he kept them for several days. They showed no in- 

 clination to scrape, . . . but when Dr. Thomson sprinkled 

 a little gravel on the carpet, . . . the chickens immediately 

 began their scraping movements." :{: A strange person, and 

 darkness, are both of them stimuli to fear and mistrust in 

 dogs (and for the matter of that, in men). Neither circum- 



* Archiv f. d. ges. Physiol., Bd. 26, p. 176 (1881). Exner thinks {ibul 

 Bd. 28, p. 497 (1882) ) that the summation here occurs in tlie spina) cord. 

 It maki.'S no difference where this particular summation occurs, so far as 

 the general pliilosophy of summation goes. 



t G H. Lewes : Physical Basis of Mind, p. 479, where many similai 

 examples are yiven, 487-9. 



t Romanes : Mental Evolution in Animals, p. 163. 



