CHAP. XI.] POLAR STATE OF THE CORD. 315 



warm-blooded classes. Hence there is an objection to the use of 

 opium in large doses in cases of tetanus ; and experience has shewn 

 its utter inefficacy when administered to a large amount. 



This polar state of the cord, at least of a part of it, is sometimes 

 developed naturally. The most remarkable example of this with 

 which we are acquainted is in the case of the male frog, in the 

 spring of the year, the season of copulation ; the thumb on each 

 hand becoming at this season considerably enlarged, as is well 

 known to naturalists. This enlargement is caused principally by a 

 considerable development of the papillary structure of the skin 

 which covers it, so that large papillae are formed all over it. A 

 male frog at this season has an irresistible propensity to cling 

 to any object by seizing it between his anterior extremities. It is 

 in this way 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 expelled. An effort of the 

 will alone could not keep up such a grasp uninterruptedly for so 

 long a time ; yet so firm is the hold, that it can with difficulty be 

 relaxed. Whatever 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 wood, or a 

 dead fish, or some other substance which they may chance to meet 

 with. If the finger 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 

 finger is within the grasp of its anterior extremities, they still con- 

 tinue 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 segment of the cord from which the 

 anterior extremities derive their nerves has been removed, all 

 their motion ceases. This curious instinct, then, of the male frog, 

 which naturalists have long noticed, is evidently connected with 

 an exalted polarity of the cord, which is most manifest in the 

 anterior extremities by reason of the enlargement of the thumb. 

 It only exists during the period of sexual excitement ; for at other 

 periods the excitability of the anterior extremities is considerably 

 less than that of the posterior. 



Nothing seems to control this polar state of the cord so effect- 

 ually as cold. Ice applied along the spine, or the cold douche, 

 may be frequently employed with great advantage in cases of 

 muscular disturbance dependent on this polar state of the cord. 

 AVe know of no substance which, when introduced into the blood, 



