816 THE POPULAR SCIENCE MONTHLY. 



motor nerves, is transformed into movements of the muscles, which 

 then become the exterior and visible signs of the emotion. A burn on 

 the finger produces a contraction of the features. A lively joy or a 

 deep disquiet throws us into a condition of agitation and purposeless 

 talking and moving about. If the emotion is concentrated, the cere- 

 bral disturbance increases in violence as the muscular agitation dimin- 

 ishes. When we spend the excess of our agitation in external move- 

 ments, in gestures, walking back and forth, tears, and lamentations, 

 the cerebral agitation is correspondingly diminished. These phenom- 

 ena of diversion are nothing else than particular cases of the conserva- 

 tion of force and the propagation of movements. Sometimes the 

 propagation results in a real metamorphosis. Very violent emotions, 

 producing a reaction on the central parts of the innervation, bring on 

 a sudden paralysis of a number of muscular groups, while feeble dis- 

 turbances of the sensibility produce superexcitation, which is subse- 

 quently replaced by exhaustion. This is what Wundt calls the law of 

 the metamorphosis of nervous action. There result from it effects of 

 balancing and compensation which, in our opinion, are still simply an 

 application of the law of equivalence between movements. 



M. Mosso's physiological explanations usually revert into Wundt's 

 law, and with stronger reason into the general law of the equivalence 

 of forces. He has shown that cerebral excitation makes the blood 

 flow to the brain, and that, during intellectual labor, the afflux is 

 sufficient to diminish the volume of the arm. He observed the cir- 

 culation of the blood in three subjects whose craniums had been par- 

 tially destroyed. Whenever a stranger came in, or a sudden noise was 

 heard, the cerebral pulse rose immediately. Under the influence of 

 fear the blood flows back to the extremities, to such an extent that a 

 ring can not be pulled off from the finger. M. Mosso has also applied 

 the balance to the study of the circulation. A man is laid full length 

 in a wooden box, arranged as a balance upon a knife-edge, with appa- 

 ratus for marking the trace of the pulse in the feet and hands, and the 

 changes of volume undergone by these organs. When the balance and 

 the man in it are in equilibrium and repose, something is said to the 

 man. Instantly, by the effect of the excitation received and the at- 

 tention responding to it, the balance inclines toward the man's head. 



Mr. Warner has carefully studied the effects of the emotions in 

 nutrition, which he calls the trophic signs. Maladies that modify 

 nutrition also modify the nervous system, and render it more irritable. 

 The poorly-nourished child often has what the doctors call the nerv- 

 ous that is, shaky hand ; a more reduced nutrition may end in 

 chorea. Plants also afford examples of excessive irritability, arising 

 from imperfect nutrition. Some sensitive plants were sowed in clear 

 sand, and others in vegetable mold mixed with sand in different pro- 

 portions. The first, which had nothing but air to feed upon, lan- 

 guished and died ; they were extremely sensitive to the lightest touch ; 



