KNOWLEDGE ♦ 



5BIT. 1, 1882. 



ao m&intainlng the constancy of the cell. The two side 

 ohainlH-rs ar* called "idle" cells, as the zinc plate and 

 porous pot are placed in tlieni when the cell is not working. 

 Tht' KSI.F of this standard is a little more than one volt — 

 vir . 1 -079. 



A POISONOUS LIZARD. 



J!v Dr. Asdbew Wilso.v, F.R.S R, F.L.S. 



'PHE poii-session of a poison-apparatus is liy no means a 

 X connium event in tht^ animal world ; although, indeed, 

 very diverse animals are possessed of otl'cnsive means of 

 this kind. Low down in the animal scale we find the 

 jelly-fishes, sea-anemones, and their neighhours, possessing 

 these curious stinging organs called " thread-cells," the 

 virulence of which many an unwary liather has experienced 

 to bis cost. Each thread-cell is really a minute bag, 

 tensely filled with fluid, and containing, coiled up in its 

 inte.rior, a thread or filament. When, from any cause — as 

 l>y pressure, for example— the cell is ruptured, the fluid 

 e.wapes, and if the thread and fluid together come in contact 

 with the tissues of any animal liahle to be airectcd, the 

 animal in question will Iw paralysed, cr even killed. In 

 tlii.s way the Hylra, or " fresh-water polype," captures its 

 prey ; and even in the lower deeps of the animal world 

 (as amongst the I»/iisutiit, for example), these thread-cells 

 appear to be represented. Higher up in the animal series, 

 we come upon the poison-apparatus of insects, carried in 

 their tails, as also is the "sting" of the scorpion. The 

 centipede's poison-fangs are situated, on the contrary, in 

 its mouth. Amongst the shellfish, or J/o//«.sr»-, no poison- 

 secretions occur. In fishes, as the lowest Vertebrates, wo 

 certainly know of one or two cases in which an approach 

 to a poi.son-apparatus is found. The frogs and toads, "ugly" 

 as they may Ik-, are yet not " venomous," .Shakespeare not- 

 withstanding. Acrid and irritating secretions may bo 

 poured out from the skin-glands of these animals. Such 

 secretions are seen typically developed in the toads ; but 

 they are not " poisonous," in the common sense in which we 

 u.se that term. 



It is in the chiss of reptiles that the venomous attains 

 its full development. Here, in the group of the snakes, 

 we reach the acme of poison evolution. A typically 

 poi.sonous snake, like the Rattlesnake or Viper, possesses 

 two elongated and hollow " fangs," borne on its upper jaw. 

 Tli'-ge fangs are merely largely-developed teeth, and their 

 hollow i:it*rrior3 each communicate by means of a canal 

 with the poi.son gland. This gland, placed in front of 

 and below the eye on each side, is merely a modified 

 tnlivartj ijUiri'l, and corresponds to that gland in man 

 known as the pnrotiJ, and which becomes enlarged in 

 children suffering from " mumps." It is highly int'-resting 

 to find that whilst the poison-secretion of a snake is 

 nifrdy permanently modified salira, we know of cases 

 among qua'lrupeds in which the fluid of the mouth becomes 

 ti'mporarily vinomou.s. The case of the rabid dog is the 

 iiio^t familiar example of this fact ; and it is curious to re- 

 flect on the similarity in nature which exists between tin; 

 virufi of animals so widely separated as are snakes and 

 innmnaala. 



The clavs of lizard.H is well known to be related to that 

 of the snakes hj many ties of structural kinship. Both 

 are groufjs of the reptilian class, and we find certain 

 lizards {e.g., the harmless blind worm of Britain), which 

 may be as destitute of legs as any snake. No lizard, until 

 within a few days since, was known to be poisonous, or to 

 pfjywiui any structures suggestive of the poseession and 

 manufact'ire of a poisonous secretion. Horrible, ungainly 



and ugly as many lizards are, no fear of evil consequences 

 could have been experienced in handling them, and 

 naturalists would have given a very decided negative to 

 any inijuiry respecting the existence of a poison-secretion 

 in the lizard group. But as it is the unexpected which 

 happens proverbially in political and social life, so 

 zoological existence has been startled by the news that a 

 truly poisonous lizard has at length been discovered. 



This lizard is named the Unhdirma horrida, and hails 

 from the neighbourhood of Puebla. It is, therefore, a 

 denizen of the New World, and has found its way to the 

 reptile house in the London Zoo' through the kindness of 

 Sir John Lubbock. The traditions of the lizard are, it 

 appears, unfavourable, if its Indian character is to be 

 believed. The natives appear to regard it as a malignant 

 deity, and are said to endeavour to propitiate the .supposed 

 evil power by the ofler of sacrifices to the lizard god. When 

 first brought to London, the reptile was regarded as an 

 interesting example of a rare species of lizard. Like the 

 rest of its V)rethren, it was b<>lieved to be thoroughly and 

 completely harmless. True, stories had now and then 

 been circulated by travelleis in Mexico, that there existed 

 in that country a lizard, or reptile of allied nature, whose 

 bite was believed to be terribly fatal. But naturally 

 enough, without evidence of the existence of such an 

 animal, naturalists relegated the story to the domain of 

 legend and exaggeration. Without direct evidence of such 

 a statement, no man of science, basing his knowledge of 

 lizard-nature on the exact knowledge to hand, would have 

 hesitated in rejecting the story as, at least, improbable. 

 Yet it is clear that the stories of the New World may have 

 had an actual basis of fact ; for the llalodcrmn horrida 

 has been, beyond doubt, jiroved to bo poisonous in as high 

 a degree as a cobra or o rattlesnaki>. 



At first the lizard was frei^ly handled by those in charge 

 at Regent's Park, and being a lizard, was regarded as 

 harmless. It was certainly dull and inactive, a result pro- 

 liably due to its long voyage and to the want of food. 

 Thanks, however, to the examination of Dr. (Jiinthcr, of 

 the British Museum, and to actual experiment, we now 

 know that llidoirrma will require in future to be classed 

 among the deadly enemies of other animals. Examjning 

 its mouth. Dr. Giinther found that its teeth formed a literal 

 series of poison-fangs. Each tooth, apparently, possesses 

 a poison gland ; and lizards, it may be add(!(l, are plen- 

 tifully supplied with these organs as a rule. Experimenting 

 upon the virulence of the poison, llalodnrma was made to 

 bite a frog and a guinea pig. The frog died in one nlinut^ 

 and the guinea-pig in three. The virus required to pro- 

 duce these eli'ects must be of singularly acute and powerful 

 nature. It is to be hoped that no case of human mis- 

 adventure at the teeth of Halnderina may happen. There 

 can be no question, judging from the analogy of serpent- 

 bit(^ that th<-' poison of the lizard would aflect man. The 

 sacrifice of a guinea-pig and a frog may be, and most pro- 

 bably will be, cited by rabid anti-vivisectionists as a cruel 

 experiment Sensible persons will apply another term to 

 the test whereby the virulence of the lizard was esta- 

 blished, and humanity thereljy placed on its guard. Fore- 

 warned is forearmed, whether we consider the case of a 

 burglarious attack on our premises, or the bite of a lizard. 



i 



Ark Toaph I'oisonois ? The Inrgo wart-liko (flimdH on the heaH 

 and lj!ick of tho toad Hccretc ii tliick, yellowisli-wliito lluid of nii 

 cxcoedingly ncrirl and offcnHivo nntiiro. If thoHO glamlM iiro Hqnoezed 

 or roughly handle'', tho secretion JH oxudcd through ii inimbor of 

 j)orcs, like pin-holcH, in tho snrfaco of tho ghmdH. Nn douht it iH 

 owing to this fact that the toad had gained ils niiinc m a vcnomoim 

 reptile.- W. B. Wkken. 



fl 



