v SPINAL COED AND NERVES 335 



of the trophic influence of the nerves and their corresponding 

 centres. 



But this trophic influence must not be taken in the sense 

 previously suggested by Meissner and Samuel, viz. that there is 

 a special category of trophic nerves and centres, entirely distinct 

 from the sensory and the motor, whose function is the direct 

 control of metabolism and nutrition of the tissues, independently 

 of both the blood and lymph circulation, and of the new conditions 

 of functional paralysis set up in the tissues after the section or 

 lesion of their respective nerves. Any such hypothesis, besides 

 being unsupported by experimental facts, is contrary to the spirit 

 of the cell theory, according to which the function of living 

 cells is inseparable from their nutrition, because every excitation 

 necessarily has an altered metabolism for its material basis. 

 When the function of a cell or organ is under the direct and 

 absolute influence of another cell or organ (as the muscle depends 

 upon the nerve), then the latter by controlling the function must 

 also indirectly control the nutrition of the former. 



XI. In discussing the spinal reflexes we saw that there is a 

 certain relation between the sensory surface stimulated and the 

 reflex. In a spinal (or bulbo-spinal) animal direct stimulation 

 of the central end of a large nerve only evokes a spasmodic unco- 

 ordinated reflex, in which muscles of different or even antagonistic 

 function are simultaneously thrown into action ; on stimulation of 

 a sensory surface, on the contrary, the combination of the muscles 

 thrown into play is much more complex, and the reflex is repre- 

 sented by a true co-ordinated motor act, in which not only do 

 many muscles take part, but there is an evident harmony between 

 the strength, duration, and precise moment of the contraction of 

 each muscle that participates in the action. In fact, the expression 

 " co-ordinated muscular act " means that the whole movement is 

 directed towards the attainment of a useful effect in the most 

 profitable manner, and that the muscular reaction is perfectly 

 adapted to the stimulus, so that there is an ideal teleological 

 relation between them. 



Grainger (1837) seems to have been the first who pointed out 

 that the reflex spinal movements excited by cutaneous stimuli 

 were defensive in character, and apparently directed to the purpose 

 of removing the stimulus. 



The most classical example of these defence reflexes of force is 

 seen in the spinal or bulbo-spinal frog. The crouching position 

 that it naturally assumes shews that the spinal centres are in 

 continuous activity, because a paralysed animal stays in any 

 position given to it. If the leg is pinched, it is drawn away as 

 though to escape from a painful impression. If a bit of paper 

 soaked in dilute sulphuric or acetic acid is applied to any point 

 of its skin, the frog performs a whole series of movements, which 



