316 PHYSIOLOGY CHAP. 



stimulated the irradiation is from left hind-limb to left fore-limb, 

 tail, right hind-limb, right fore-limb. 



Generally speaking, we may accept Sherrington's statement 

 that the reflexes from spinal animals are very analogous to those 

 obtained from normal animals. The latter of course exhibit 

 greater variability in their reflex reactions. The long spinal 

 reflexes are generally more variable and less constant than the 

 short reflexes. 



From this discussion it will be seen that Pfliiger's laws now 

 have little more than a historical interest, owing to the exceptions 

 discovered to them. If any general rules for the origin and spread 

 of reflexes are to be formulated it is all-essential to take their 

 "biological significance" (Langendorff) into account, as deduced 

 from the fact that they almost always represent a reaction co- 

 ordinated to a given end, and useful to the organism as a whole. 



Bagiioni (1904-7), who analysed the reflexes that can be 

 obtained from the "spinal frog" after the bloodless severance of 

 the medulla oblongata (compression by a clamp), when the animal 

 can survive for a long time, was able to demonstrate that different 

 retiex mechanisms exist potentially in the spinal cord, the 

 manifestation of which depends not so much upon the seat, the 

 intensity, and the duration as upon the nature of the peripheral 

 stimulus. Gentle pressure with the finger or other blunt object 

 on the sole of the foot excites an extensor reflex of the hind- 

 liinb with spread of the toes of the same foot, so that the web 

 presses against the impinging finger (plantar reflex). Painful 

 stimulation (e.g. electrical, chemical, mechanical, pricking with the 

 point of a pin, or compression with forceps) of the same point of 

 the skin evokes the opposite reflex, i.e. flexion of the hind-limb 

 and contraction of the web, so that the foot is moved always from 

 the stimulus and the limb drawn up to the body. 



Similar reflexes have been demonstrated by Sherrington (1904) 

 on the "spinal dog," by Bagiioni and Matteucci (1909) on the 

 "spinal pigeon," and by G. Cesana (1911) on rats after the three 

 first days of life. (In the earliest hours of life the rat always 

 responds by a movement of flexion (Cesana).) 



On the strength of these facts Bagiioni distinguishes two 

 classes of reflex actions: those due to abnormal injurious stimuli, 

 and those due to normal (biological or functional) stimuli. 



(</.) In the first class the reflex movements are in proportion to 

 the strength and duration of the stimuli. If these are weak or of 

 short duration, the reflex aims at removing the point of the body 

 abnormally stimulated ; if they are strong or protracted, this 

 movement is succeeded by more complicated reflexes directed to 

 remove the obnoxious stinmlus. 



(&) The reflexes of the second class are in relation, not with the 

 strength or duration, but with the nature of the stimulus, which is 



