THE SCOPE OF PSYCHOLOGY. 9 



but such mere outward teleology as tins might still be the 

 blind result of vis a tergo. The growth- and movements of 

 plants, the processes of development, digestion, secretion, 

 etc., in animals, supply innumerable instances of per- 

 formances useful to the individual which may nevertheless 

 be, and by most of us are suppos«^d to be, produced by 

 automatic mechanism. The physi >logist does not con- 

 fidently assert conscious intelligence in the frog's spinal 

 cord until he has shown that the useful result which the 

 nervous machinery brings forth under a given irritation 

 remains the same ivhen the machinery is altered. If, to take 

 the stock instance, the right knee of a headless frog be irri- 

 tated with acid, the right foot will wipe it off. When, how- 

 ever, this foot is amputated, the animal will often raise the 

 left foot to the spot and wipe the offending material away. 



Pfliiger and Lewes reason from such facts in the follow- 

 ing way : If the first reaction were the result of mere machin- 

 ery, they say ; if that irritated portion of the skin discharged 

 the right leg as a trigger discharges its own barrel of a shot- 

 gun ; then amputating the right foot would indeed frustrate 

 the wiping, but would not make the left leg move. It would 

 simply result in the right stump moving through the empty 

 air (which is in fact the phenomenon sometimes observed). 

 The right trigger makes no effort to discharge the left barrel 

 if the right one be unloaded ; nor does an electrical ma- 

 chine ever get restless because it can only emit sparks, 

 and not hem pillow-cases like a sewing-machine. 



If, on the contrary, the right leg originally moved for the 

 purpose of wiping the acid, then nothing is more natural 

 than that, when the easiest means of effecting that purpose 

 prove fruitless, other means should be tried. Every failure 

 must keep the animal in a state of disappointment which 

 will lead to all sorts of new trials and devices ; and tran- 

 quillity will not ensue till one of these, by a happy stroke, 

 achieves the wished-for end. 



In a similar way Goltz ascribes intelligence to the 

 frog's optic lobes and cerebellum. We alluded above to the 

 manner in which a sound frog imprisoned in water will dis- 

 cover an outlet to the atmosphere. Goltz found that frogs 

 deprived of their cerebral hemispheres would often exhibit 



