634 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



observed that a slight irritation applied to the peripheral extremities of the 

 afferent nerves, is a more powerful excitor of reflex action than a much 

 stronger impression, which occasions acute pain, applied to their trunks; 

 thus Mr. Grainger found that he could remove the entire hind leg of a 

 Salamander with the scissors, without the creature moving, or any muscular 

 contraction being produced, if the Spinal Cord had been first divided ; yet 

 that by irritation of the foot, especially by heat, in an animal similarly cir- 

 cumstanced, violent convulsive actions were excited in the legs and tail. 

 This fact is important, not only as showing the comparatively powerful 

 effect of impressions upon the cutaneous surface, but also as proving how 

 little relation the amount of reflex action has to the intensity of sensation. 

 The different kinds of reflex action have been well formulated by M. Kiiss. 1 

 They may be classified according to the direction in which both the centrip- 

 etal and the centrifugal impulse passes. 1. All ordinary reflex actions take 

 place both ceutripetally and centrifugally through spinal nerves, examples 

 being afforded in deglutition, coughing, sneezing, walking, etc., and in 

 pathology by vomiting, tetanus, epilepsy. 2. A second class almost as nu- 

 merous includes those reflex actions which take place ceutripetaily through 

 a cranio-spiual nerve, and centrifugally through a motor nerve of the sym- 

 pathetic system, and most frequently a vaso-motor branch. As examples 

 of this kind of reflex action may be given the excitation of the salivary 

 and gastric glands, blushing or pallor of the skin, erection, certain move- 

 ments of the iris, certain modifications in the beats of the heart, and, in 

 pathology, some of those phenomena which in consequence of the difficulty 

 of explaining their production, are called metastatic, as certain forms of 

 ophthalmia, orchitis, and coryza, due to reflex hypememia, and certain cases 

 of amaurosis, paralysis, paraplegia, etc., due to reflex amemia. 3. A third 

 class comprehends those reflex actions in which the centripetal nerve is a 

 sympathetic nerve, and the centrifugal a cranio-spiual. Most of these ac- 

 tions are pathological, and are represented by the convulsions that occur 

 from the intestinal irritation produced by worms, reflex eclampsia, hysteria, 

 etc. A physiological instance of this form occurs in respiration, the vagus 

 or sensory nerve being a kind of transition nerve, bridging over the interval 

 between the sympathetic and the cranio-spinal nerves, so far as its pulmo- 

 nary branches are concerned. 4. Lastly, there are reflex actions in which 

 both the centripetal and centrifugal conductors are branches of the sympa- 

 thetic system. Such are the obscure actions that preside over the secretion 

 of the intestinal juices, those which unite the various generative functions, 

 the dilatation of the pupils owing to worms, and many pathological pheuom- 



cling to any object, by seizing it between his anterior extremities. It is in this way 

 that he seizes upon, and clings to the female; fixing his thumbs to each side of her 

 abdomen, and remaining there for weeks, until the ova have been completely ex- 

 pelled. An effort of the Will alone could not keep up the grasp uninterruptedly for 

 so long a time ; yet so firm is the hold, that it can with ditliculty be relaxed. What- 

 ever is brought in the way of the thumbs, will be caught by the forcible contraction 

 of the anterior limbs; and hence we often find frogs clinging blindly to a piece of 

 woud, or a dead fish, or some other substance which they may chance to meet with. 

 If the linger be, placed between the anterior extremities, they will grasp it firmly; 

 nor will they relax their grasp until they are separated by force. If the animal be 

 decapitated whilst the linger is within the grasp of its anterior extremities, they still 

 continue to hold on firmly. . The posterior half of the body may be cut away, and 

 yet the anterior extremities will still cling to the finger; but immediately that the 

 segment of the Cord, from which the anterior extremities derive their nerves, has 

 been removed, all their motion ceases. This curious instinct only exist* during the 

 period of sexual excitement; for at other periods the excitability of the anterior ex- 

 tremities is considerably less than that of the posterior." 

 1 Cours de Physiologic, 1873, p. 02. 



