180 ANIMAL AMIDES. 



SECTION I. OF ALBUMEN. 



The term albumen employed by Pliny to denote the white 

 of an egg,* began, about the end of the last century, to be 

 applied to certain organic substances, which have the property 

 of coagulating, when heated to the temperature of 159. In 

 their natural state they are soluble in water, but lose this solubi- 

 lity by coagulation. The word albumen does not occur in the- table 

 of the new chemical nomenclature, published by the French che- 

 mists in 1787. But we find it employed by Fourcroy about the 

 year 1789.f He and Vauquelin seem to have been the first che- 

 mists that attempted to fix its meaning with something like preci- 

 sion. Albumen may be obtained sufficiently pure from the white 

 of an egg and from the serum of blood. 



When healthy blood is drawn from an animal, and left at rest, 

 it gradually separates into two portions ; namely, a gelatinous- 

 looking substance, containing all the red globules, and called the 

 cras&amentum or clot, and a liquid portion of a greenish-yellow 

 colour, which floats over the clot. This liquid is called the se- 

 rum of the blood. 



It was first observed by Dr Harvey, that when serum is heat- 

 ed, it coagulates, and becomes as firm as the coagulated white of 

 an egg, though not so white.f The coagulating point, as deter- 

 mined by my thermometer, is 159. It has been long known that 

 the white of an egg coagulates when heated to the same point. 

 Rouelle and Bouquet, about the year 1776, first compared serum 

 of blood and white of egg together, and concluded that both con- 

 tained a similar substance. To this substance, as has been al- 

 ready stated, the name albumen was applied, from a notion (now 

 known to be erroneous), that it existed in the state of greatest pu- 

 rity in the white of an egg. 



The white of egg was examined with some care by Neumann, 

 who ascertained its property of being coagulated by heat, alco- 

 hol, and acids ; found that, in a gentle heat, it might be evapo- 

 rated to dryness, leaving a yellowish translucent substance, re- 

 sembling amber in appearance, and still capable of dissolving in 

 cold water. When thus dried, he found that 100 parts of albu- 



* Plinii Hist. lib. xxviii. c. 6. f Ann de Chem. iiL 252. 



\ De Generatione Anim. p. 161. 



