138 



KNOWLEDGE 



[June 1, 1894. 



impaired by being heated to 79° C, and that death occurs 

 as rapidly as when the unheated ] oison is used, but Fayrer 

 and Wall noted that prolonged boiling completely destroyed 

 its power. Alcohol, often spoken of as an antidote, has 

 been shown to have absolutely no effect on the venom, and 

 is only of use as a general stimulant to the system after a 

 bite from a serpent. Mineral acids and the caustic 

 alkalies neutralize it, but alum, though it delays, does not 

 prevent death. The most active neutralizing agents yet 

 known are potassium permanganate, ferric chloride, and 

 iodine, especially the first ; but owing to the rapidity with 

 which the venom circulates through the system they could 

 only be of local use, and would be of little avail once the 

 poison were absorbed. 



Taken internally, the poison is as a general rule harm- 

 less, unless there be some abrasion by which it can get 

 into the blood. The same applies also to its action on 

 other mucous surfaces. Fayrer mentions a case where 

 one of his assistants accidentally got seme of the venom 

 into his eye, with no worse result than temporary inflam- 

 mation. Its primary action on the respiratory system is 

 first to cause an increase in the number of respirations 

 and then to diminish their number. Under its influence 

 the blood corpuscles lose their shape and become fused 

 together and the blood becomes incoagulable. Its 

 action on the nervous system is, comparatively speaking, 

 unimportant, and death occurs from paralysis of the 

 respiratory centres or from inability of the blood cor- 

 puscles to do their work. The terrible local changes 

 which occur after death from the bite of a rattlesnake are 

 much less noticeable in the case of the cobra. 



Among the most interesting properties of the venom is 

 its action on other snakes. Sir Joseph Fayrer on more 

 than one occasion caused a cobra to bite its own tail, 

 which it would do very readily, but beyond the local 

 wound it suffered no ill consequences. Cobras were found 

 also to be immime against the bite of other cobras, but 

 non-venomous snakes succumbed as rapidly as warm- 

 blooded animals. The Indian viper, the Daboia, whose 

 bite is as dreaded as that of the cobra, was found to be 

 proof against the venom, and other species of poisonous 

 snakes more or less so, apparently according to the strength 

 of their own venom. It would thus seem that there is in 

 the blood of the more poisonous snakes some principle 

 which renders the venom innocuous, and in this direction 

 may lie the possible discovery of an antidote. 



RIB-WALKERS." 



By E. Lydekker, B.A.Cantab. 



TO say nothing of invertebrates, among which the 

 range of diversity is still more extensive, a great 

 difference prevails among vertebrate animals in 

 regard to the mode of progression, although 

 movements of this nature are nearly always effected 

 by means of the limbs. Ordinary mammals and reptiles, 

 for instance, either walk or run by using both pairs of 

 limbs ; but in birds and kangaroos, as well as in some of 

 the extinct dinosaurian reptiles, progression on land is 

 effected by the hinder pair alone, aided in some cases 

 by the tail. Jerboas and gerbils, as well as some other 

 rodent mammals, have likewise taken to a saltatorial 

 mode of progression ; while frogs mainly progress by 

 means of leaps effected by the elongated hind legs. Other 

 mammals, agam, are capable of making long flying leaps 

 by the aid of parachute-like expansions of skin along the 

 flanks and limbs ; while the bats and most birds, together 

 with the extinct pterodactyles, alone have the fore 



limbs so modified as to subserve the purpose of true flight. 

 Then we may have both pairs of limbs converted into 

 paddle-hke flippers for swimming, as in the seals among 

 mammals, and turtles in the reptilian class ; while in 

 other cases, as in the whales and porpoises, only the fore 

 limbs are thus modified, while the hinder pair are 

 aborted, the tail being also adapted to act both as a kind 

 of screw-propeller and as a rudder. In fishes, on the 

 other hand — in which, from its vertical position, the tail is 

 a decidedly more rudder-like organ — both pairs of limbs are 

 used in swimming, and are aided by various paired and 

 unpaired fins, which have no connection with the latter. 

 Aquatic birds which float solely on the surface of the 

 water employ their hind limbs only in swimming, although 

 when diving many of them use their wings to a greater or 

 less degree ; but in the penguins the wings have become 

 modified into paddles pure and simple, and are only used 

 in diving. Frogs seem to be almost, if not quite, peculiar 

 in using only the hind pair of Umbs when swimming. 



In all these instances, it will be noticed, progression is 

 effected either entirely or mainly by one or both pairs of 

 limbs ; but there are certain groups of vertebrates in which 

 limbs have more or less completely disappeared, and where 

 other means of progression have consequently to be em- 

 ployed. Among terrestrial types, the only completely, or 

 even practically, limbless forms are the various groups of 

 snakes, together with certain snake-like creatures, such as 

 the familiar blind-worm and some of the skinks, which, 

 although ordinarily denominated snakes, are in reality 

 nothing more than specially modified lizards, which have 

 assumed a snake-like form. 



Although these snake-like lizards creep merely by a 

 kind of wriggling motion along the ground, the majority 

 of real snakes progress by means of a special modification 

 of structure, which is, perhaps, the most unique and pecu- 

 liar that could well have been hit upon by creatures 

 hampered by having to adhere to the vertebrate type of 

 structure. Snakes in general may be in fact not inappro- 

 priately termed "rib-walkers," since their ribs are the main 

 instruments of progression ; and in thus making use of 

 the whole length of their body and tail for this purpose 

 they may be compared to worms and certain other sym- 

 metrically segmented invertebrates, where every joint of 

 the body takes its share in this function. As most of us 

 are probably aware, in mammals true ribs are compara- 

 tively few in number, and are limited to a portion of the 

 region of the trunk. If, however, we examine the skeleton 

 of a snake, we shall observe, m the first place, that the 

 number of joints, or vertebrse, in the backbone is exceed- 

 ingly large, and that each of these joints, from the head 

 to a considerable distance down the tail, is provided with 

 a pair of curved and relatively long ribs, upon the extremi- 

 ties of which the skeleton rests. While comparatively 

 short in the region of the neck, these ribs gradually 

 increase in length towards the anterior part of the trunk, 

 and thence diminish by almost imperceptible degrees as 

 the tail is approached. As showing the extraordinary 

 amount of elasticity of which the vertebrate type of 

 organization is capable without the loss of its main dis- 

 tinctive features, we may contrast the skeleton of a snake 

 with that of a frog, when we shall find that whereas the 

 one attains the maximum development in the way of ribs, 

 the other has these structures reduced to a minimum. 

 In fact, for all practical purposes, a frog may be described 

 as a ribless creature ; the ribs being represented by small 

 rudimentary bones attached to the extremities of long 

 horizontal processes standing out from the sides of the 

 vertebrae. And it may be incidentally mentioned that in 

 consequence of this practical absence of ribs, a frog cannot 



