834 THE SPINAL CORD. 



apparatus, e.g. joints and muscles considered as sources of centripetal 

 impulses, as well as to the skin. The evidence is, however, scanty. The 

 assumption of posture by the spinal frog goes far, I think, toward 

 establishing it. The spinal frog, if gently left under a bell-jar with 

 one hind-limb extended, is found in the course of a variable time to 

 have drawn the limb into flexion ; and this it does when the skin of 

 the limbs has been removed. Bethe's observations on insects show that 

 reflex correction of the inverted position after decapitation is a contact 

 reflex. The muscular unrest of a spinal frog (transection behind the 

 eighth cranial nerve), when first inverted, is suggestively greater than 

 when a piece of wood of weight equal to the frog rests upon the dorsal 

 skin. 



In connection with localising power and local sign and spinal reflexes, 

 there is the widespread occurrence of stereotropic reactions in spinal animals, 

 as already referred to ; such reactions imply localisation. Thus the headless 

 eel and Amphioxus swim " upright," the amputated ray of the starfish 

 rapidly rights itself when inverted on a solid surface, 1 and is restless 

 when its ambulacral feet are not in contact with something firm. After 

 removal of the cephalic ganglia, Grillotalpa and many insects, also Astacus, 

 resist inversion and maintain the body's equilibrium. The balancing compen- 

 sating movements of the tail of the bird 2 after spinal transection, and the 

 series of movements by which Ceriantlms when inverted in a test-tube re-erects 

 itself, are other instances. 3 



Fatality of spinal reflexes. — The movement resulting from each 

 one of a series of slowly repeated stimuli applied under as far as 

 practicable similar conditions to an afferent channel in a spinal animal, 

 remains often approximately similar through a long series. It can be 

 fairly predicted that the second response will be very like the first. 

 The uniformity of response is, as might be expected, best marked in the 

 simplest reflexes, e.g. such as may be obtained from quite limited 

 isolated fractions of the cord. In them the possible paths are most 

 reduced, and the numbers of links (nerve cells) composing the nervous 

 chains are smallest, — in other words, the synapses are fewest ; in some, 

 perhaps, there intervenes but one synapsis. These reflexes are the 

 most " fatal," but their " fatality " is widely removed from absolute. 

 It does not approach that with which similar movements follow repeated 

 similar excitations of a motor nerve. In the frog the successive similar 

 stimulation of a spot of skin, say on the second pedal digit, may regularly 

 evoke flexion of the knee and ankle ; but with that flexion may or 

 may not be combined flexion of hip, and the degree of dorsal flexion of 

 the digits will vary. 



The fatality of reflexes might be logically inferred from what Grainger 4 

 described as their "resemblance to the motion which the function of the organ 

 requires." In the intact complete individual the reaction of one part is as a 

 rule subordinated to the advantage of the individual as a whole. The isolated 

 local nervous system of spinal rank executes, so to say blindly, its special 

 reaction uninfluenced by the condition of other parts of the nervous system. 

 Michael Foster 5 has pointed out that when the normal Astacus laid 

 over on its back is trying to correct its posture, an object, even food, placed 



1 Romanes, op. cit. ; also Preyer, Demoor, Loeb, and others. 



2 Singer, SUzungsb. d. k. Akad. d. Wissensch., Wien, 1884, Bd. lxxxix. 



3 Loeb, Arch./, d. qes. Physiol., Bonn, 1895, Bd. lix. 



4 "Functions of the Spinal Cord," London, 1837, pp. 3, 101. 

 6 In Huxley's "Crayfish," London, 1880, pp. 110, 111. 



