90 



AMPHIBIA. 



men and calomel. Nitrate of silver, muriate 

 of gold , and of platinum , also precipitate album i- 

 nous solutions. These precipitates are mostly 

 triple compounds of acid, albumen, and oxide, 

 and several of them are redissoluble in excess 

 of liquid albumen. 



Albumen is precipitated by tannin in the 

 form of a yellow viscid combination. Water, 

 holding a thousandth part of solid or a two- 

 hundredth of liquid ovalbumen, becomes tur- 

 bid after some hours by the addition of a 

 solution of galls containing 2.5 per cent, of 

 solid matter. (Bostock.) 



The above are the principal chemical pro- 

 perties of liquid and solid albumen as obtained 

 from the egg and from serum of blood ; several 

 of their modifications will be noticed under 

 other heads, such as FIBRIN E, MILK, BILE, 

 &c. 



The cause of the coagulation of albumen is, in 

 many cases, obscure and even inexplicable. It ap- 

 pears possible that the acids by which it is co- 

 agulated enter into combination with it so as to 

 form insoluble compounds; the same change pro- 

 bably happens with certain metallic salts, and 

 with tan ; its coagulation by alcohol has been 

 ascribed to the abstraction of water. Having 

 remarked the copious coagulation of albumen 

 at the electro-negative pole in the voltaic cir- 

 cuit, I was induced to ascribe the fluidity 

 of albumen to combined soda, the evolution 

 of which seemed to cause its solidification, and 

 it appeared possible that the acids and even 

 alcohol might also occasion coagulation by the 

 abstraction of soda ; and that its more enigma- 

 tical coagulation by heat only, might be as- 

 scribed to the transfer of soda from the albu- 

 men to the water. It has been objected to 

 this statement that the addition of alcali to 

 coagulated albumen does not reproduce liquid 

 albumen, and that acetic acid causes no co- 

 agulation ; but when albumen is once coagu- 

 lated, its properties are essentially modified, 

 and acetic acid, or even acetate of soda appear 

 to form soluble compounds with it. (Gmelin.) 

 Dr. Turner* supposes that albumen combines 

 directly with water at the moment of being 

 secreted, at a time when its particles are in 

 a state of minute division ; but as its affinity for 

 that liquid is very feeble, the compound is 

 decomposed by slight causes, and the albumen 

 thereby rendered quite insoluble. The or- 

 ganization of albumen may certainly be con- 

 cerned in its singular properties with respect to 

 many coagulants : there are several albuminous 

 fluids, which we shall hereafter refer to, which 

 contain globules resembling thosexof the blood. 

 In the voltaic coagulation of albumen, that 

 which separates at the positive pole contains 

 globules, which, under the microscope, resem- 

 ble the blood-globules deprived of their co- 

 louring matter.f 



The readiest tests of the presence of albumen 

 in fluids are its coagulation by heat, alcohol, 



* Elements of Chemistry, 4th ed. 868. 

 t Prevost et Dumas, Ann. de Chimie et Physique 

 xxiii.52. 



and acids; when it is too dilute for such 

 detection, it may be subjected to voltaic elec- 

 tricity, or tested by corrosive sublimate, or 

 by ferrocyanate of potassa; the alcali should, 

 in the latter case, be previously neutralized 

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

 experiments, that white of egg is an antidote 

 to the effects of corrosive sublimate when taken 

 into the stomach, and that, if administered in 

 sufficient quantity immediately after the recep- 

 tion of the poison, it prevents the progress 

 of the symptoms. The white of one egg 

 appeared sufficient to render four grains of the 

 poison ineffective. 



The readiness with which some metallic 

 oxides are received into the system may per- 

 haps be ascribed to their affinity for albumen, 

 with which some of them form compounds not 

 easily decomposable, and in which the metallic 

 oxide cannot be detected by the usual tests, 

 till they have been subjected to heat sufficient 

 to decompose the organic matter. Mercury 

 and silver are thus, in certain cases, detected in 

 the secretions and excretions. 



(W. T. Brande.) 



AMPHIBIA. (A^pK, utrinque, to $, vita. 

 Fr. Amphibies. Germ. Amphibien. Ital. 

 Amphibie.) A class of vertebrated animals, 

 hitherto almost universally considered as an 

 order of REPTILIA, constituting the Batrachia 

 of the later erpetologists. To the retention 

 of the latter appellation, as derived from the 

 Greek name of a single form of the group, 

 and as bearing no reference to any character 

 either of structure or of habit, there is an 

 obvious objection. The term Amphibia is 

 therefore here adopted, as designating one of 

 the most striking peculiarities of the class; 

 namely, the change which takes place at an 

 epoch of their life, more or less advanced, 

 from an aquatic respiration by branchise to an 

 atmospheric respiration by true lungs, and 

 an equivalent and consequent alteration in 

 their general structure and mode of life. 



The Amphibia may be characterized as 

 " vertebrated animals, with cold blood, naked 

 skin, oviparous reproduction, and most of them 

 undergoing a metamorphosis or change of con- 

 dition, having relation to a transition from an 

 aquatic to an atmospheric medium of respi- 

 ration." 



These characters, by many of which the am- 

 phibia are distinguished from the reptilia, are 

 sufficiently determinate and important to justify 

 our considering them as a distinct class, ac- 

 cording to the generally received principles of 

 zoological arrangement ; notwithstanding most 

 even of the modern writers on the subject have 

 retained them as merely an order of reptilia. 

 But it will also be seen that if in the adult state 

 they approach the reptilia in many points of 

 their general structure, their organization, during 

 the early and imperfect condition of the tad- 

 pole, partakes no less of that of fishes. As 

 an osculant or intermediate form, connecting 

 two others of higher typical importance, it may 

 be, certainly of greater extent, and consisting 



