90 AMPHIBIA. 



men and calomel. Nitrate of silver, muriate and acids ; when it is too dilute for such 

 of gold, and of platinum, also precipitate albumi- detection, it maybe subjected to voltaic elec- 

 tions solutions. These precipitates are mostly tricity, or tested by corrosive sublimate, or 

 triple compounds of acid, albumen, and oxide, by ferrocyanate of potassa; the alcali should, 

 and several of them are indissoluble in excess in the latter case, be previously neutralized 

 of liquid albumen. by acetic acid. It would appear, from Orfila's 



Albumen is precipitated by tannin in the experiments, that white of egg is an antidote 



form of a yellow viscid combination. Water, to the effects of corrosive sublimate when taken 



holding a thousandth part of solid or a two- into the stomach, and that, if administered in 



hundredth of liquid ovalbumen, becomes tur- sufficient quantity immediately after the recep- 



bid after some hours by the addition of a tion of the poison, it prevents the progress 



solution of galls containing 2.5 per cent, of of the symptoms. The white of one egg 



solid matter. (Bostock.) appeared sufficient to render four grains of the 



The above are the principal chemical pro- poison ineffective. 



perties of liquid and solid albumen as obtained The readiness with which some metallic 



from the egg and from serum of blood ; several oxides are received into the system may per- 



of their modifications will be noticed under haps be ascribed to their affinity for albumen, 



other heads, such as FIBIUNE, MILK, BILE, with which some of them form compounds not 



&c. easily decomposable, and in which the metallic 



The cause of the coagulation of albumen is, in oxide cannot be detected by the usual tests, 



many cases, obscure and even inexplicable. Itap- till they have been subjected to heat sufficient 



pears possible that the acids by which it is co- to decompose the organic matter. Mercury 



agulated enter into combination with it so as to and silver are thus, in certain cases, detected in 



form insoluble compounds ; the same change pro- the secretions and excretions, 



bably happens with certain metallic salts, and ( W. T. Brande.) 

 with tan ; its coagulation by alcohol has been 



ascribed to the abstraction of water. Having AMPHIBIA. (A^<p^, utrinque, /3o$, vita, 

 remarked the copious coagulation of albumen Fr. Amphibies. Germ. Amphibien. Ital. 

 at the electro-negative pole in the voltaic cir- Amphibie.) A class of vertebrated animals, 

 cuit, I was induced to ascribe the fluidity hitherto almost universally considered as an 

 of albumen to combined soda, the evolution order of REPTILIA, constituting the Batrachia 

 of which seemed to cause its solidification, and of the later erpetologists. To the retention 

 it appeared possible that the acids and even of the latter appellation, as derived from the 

 alcohol might also occasion coagulation by the Greek name of a single form of the group, 

 abstraction of soda ; and that its more enigma- and as bearing no reference to any character 

 tical coagulation by heat only, might be as- either of structure or of habit, there is an 

 scribed to the transfer of soda from the albu- obvious objection. The term Amphibia is 

 men to the water. It has been objected to therefore here adopted, as designating one of 

 this statement that the addition of alcali to the most striking peculiarities of the class; 

 coagulated albumen does not reproduce liquid namely, the change which takes place at an 

 albumen, and that acetic acid causes no co- epoch of their life, more or less advanced, 

 agulation ; but when albumen is once coagu- from an aquatic respiration by branchiae to an 

 lated, its properties are essentially modified, atmospheric respiration by true lungs, and 

 and acetic acid, or even acetate of soda appear an equivalent and consequent alteration in 

 to form soluble compounds with it. (Gmelin.) their general structure and mode of life. 

 Dr. Turner* supposes that albumen combines The Amphibia may be characterized as 

 directly with water at the moment of being " vertebrated animals, with cold blood, naked 

 secreted, at a time when its particles are in skin, oviparous reproduction, and most of them 

 a state of minute division ; but as its affinity for undergoing a metamorphosis or change of con- 

 that liquid is very feeble, the compound is dition, having relation to a transition from an 

 decomposed by slight causes, and the albumen aquatic to an atmospheric medium of respi- 

 thereby rendered quite insoluble. The or- ration." 



ganization of albumen may certainly be con- These characters, by many of which the am- 



cerned in its singular properties with respect to phibia are distinguished from the reptilia, are 



many coagulants : there are several albuminous sufficiently determinate and important to justify 



fluids, which we shall hereafter refer to, which our considering them as a distinct class, ac- 



contain globules resembling those of the blood, cording to the generally received principles of 



In the voltaic coagulation of albumen, that zoological arrangement ; notwithstanding most 



which separates at the positive pole contains even of the modern writers on the subject have 



globules, which, under the microscope, resem- retained them as merely an order of reptilia. 



ble the blood-globules deprived of their co- But it will also be seen that if in the adult state 



louring matter.-f they approach the reptilia in many points of 



The readiest tests of the presence of albumen their general structure, their organization, during 



in fluids are its coagulation by heat, alcohol, the early and imperfect condition of the tad- 

 pole, partakes no less of that of fishes. As 



* Elements of Chemistry, 4th ed. 868. an osculant or intermediate form, connecting 



t Prevost et Dumas, Ann. de Chimie ct Physique two others of higher typical importance, it may 



xxiii. 52. be, certainly of greater extent, and consisting 



