638 EFFECT OF DRUGS OX REFLEX ACTION. 



direction of the medulla oblongata. Lastly, all the muscles of the body may be thrown into 

 contraction. 



Crossed Reflexes. There are exceptions to these rules. If the region of the eye be irritated 

 in a frog whose cerebrum is removed, there is frequently a reflex contraction in the hind limb 

 of the opposite side {Luchsingcr, Langendorff). In beheaded tritons and tortoises, and in deeply 

 narcotised dogs and cats, tickling one fore limb is frequently followed by a movement of the 

 hind limb of the opposite side {Luchsingcr). This phenomenon is called a ' ' crossed reflex " 

 (fig. 457). If the spinal cord be divided along the middle line throughout its entire extent, 

 then of course the reflexes are confined to one side only {Schiff). 



III. Extensive co-ordinated reflexes are due to stimulation of a sensory nerve, 

 causing the discharge of complicated reflex movements in whole groups of different 

 muscles, the movements being " purposive " in character, i.e., as if they were 

 intended for a particular purpose. 



Methods. The experiments are made upon cold-blooded animals (decapitated or pithed frogs, 

 tortoises, or eels) or upon mammals. In the latter, artificial respiration is kept up, and the 

 four arteries going to the head are ligatured, in order to eliminate the action of the brain {Sig, 

 Mayer, Luchsingcr). The reflexes of the lower part of the spinal cord may be studied on animals 

 (or men), in cases where the spinal cord is divided transversely in the upper dorsal region. In 

 such cases, some time must elapse in order that the primary effect of the lesion (the so-called 

 shock), which usually causes a diminution of the reflexes, may pass off. Very young mammals 

 exhibit reflexes for a considerable time after they are beheaded. 



Examples: 1. The protective movements of pithed or decapitated frogs. [If 

 a drop of a dilute acid be applied to the skin of such a frog, immediately it strives 

 to get rid of the offending body, and it generally succeeds in doing so.] Similarly, 

 it kicks against any fixed body pushed against it. These movements are so 

 purposive in their character, and the actions of groups of muscles are so adjusted to 

 perform a particular act, that Pfliiger regarded them as directed by, and due to 

 "consciousness of the spinal cord." If a flame be applied to the side or part of the 

 body of an eel, the body is moved away from the flame. The tail of a decapitated 

 triton, tortoise, newt, eel, or snake is directed towards a gentle stimulus, but if a 

 violent stimulus is used, it is directed away from it (Lucksinger). 



2. Goltz's Croaking Experiment. A pithed (male) frog, i.e., one with its 

 cerebral lobes alone removed (or one with its eyes or ears destroyed Langendorff), 

 croaks every time the skin of its back or flanks is gently stroked. [Some male 

 frogs, when held up by the finger and thumb immediately behind the fore legs, 

 croak every time gentle pressure is made on their flank.] 



3. Goltz's "Embrace Experiment." During the breeding season in spring, the 

 part of the body of the male frog between the skull and the fourth vertebra, 

 embraces every rigid object, which is brought into contact with, and gently 

 stimulates, the skin over the sternum. 



In the intact animal, the exciting stimulus lies in the degree of filling of the male seminal organ 

 ( Tarchanoff). The reflex ceases at once on gently stimulating the optic lobes {Albertoni). 



4. In mammals (dogs), the following reflex acts are performed by the posterior 

 part of the spinal cord, even after it is separated from the rest of the cord : 

 Scratching with the hind feet a part of the skin which has been tickled (just as in 

 intact animals) ; the movements necessary for emptying the bladder and for 

 defalcation, as well as those necessary for erection ; the movements necessary for 

 parturition (Goltz, Frevsberg and Gergens). Co-ordinated movements do not, as a 

 rule, occur simultaneously in portions of the spinal cord lying widely apart after 

 removal of the medulla oblongata. According to Ludwig and Owsjannikow, the 

 medulla oblongata perhaps contains a reflex organ of a higher order, which forms, 

 as it were, a centre for combining, through the medium of the nerve-fibres, the 

 various reflex provinces in the spinal cord. 



5. Co-ordinated reflexes may occur in man during sleep, and during pathological 

 comatose conditions. 



Most of the movements which we perform while we are awake, and which we execute uncon- 



