Chap, hi.] OF MOVEMENTS IN THE ANIMAL KINGDOM. 357 



cardiacal muscular tissue ; for example, the upas tieute, digitaline, 

 and so on. 



From what precedes it results that there is no essential differ- 

 ence in the contractions, whatever the excitant may be which 

 has provoked them. Little it matters whether this excitant is 

 mechanical, chemical, physical or physiological. But there are 

 individual differences in the muscles ; all are not equally sensi- 

 tive to the same excitants. The contact of an irritant chemical 

 substance, a slight puncture made with the point of a scalpel, 

 and so on, determines the contraction of most of the muscles, 

 when laid bare, of the animal life. The smooth fibres of the 

 stomach, of the intestine, &c., appear on the other hand more 

 sensitive to the variations of the temperature. The muscular 

 fibres of the scrotal dartos, the testicular cords, contract, under 

 the influence of a sudden variation of the temperatui'e, more or 

 less. The tissues with smooth fibres of the stomach, of the intes- 

 tine, seem in a certain measure to revive under the influence of 

 an elevation of the temperature. In effect, if we plunge into 

 an atmosphere of hot vapour an animal which has just died, we 

 see when the body is heated to 20 degrees, the stomach and the 

 intestines execute for half-an-hour and even an hour, peristaltic 

 movements.^ 



Light, which seems to have little or no action on any of the 

 inuscles, impresses notwithstanding the contractile fibres of the 

 iris, direct and without the succour of a reflex action. Thus two, 

 and even three, days after death the iris of eels still contracts 

 under the influence of luminous rays, provided care is taken to 

 humect the eye, and prevent its dessication. 



But the most important physical excitant, the excitant which 

 acts most surely on the smooth fibres and the striated fibres, is 

 electricity. When a muscle is maintained in suitable conditions 

 of humidity, of temperature, of medium, it contracts under the 

 influence of the continuous electrical currents and of the induced 

 cun-ents with frequent interruptions. It was with the help of 

 1 CL Bernard, loc. cit., pp. 189, 190. 



