NITEOGENOUS ORGANIC CELL-CONSTITUENTS. 93 



salts of the heavy metals precipitate serum-albumen, as do the mineral 

 acids in large quantities, especially' nitric acid. Its point of firm coagu- 

 lation is from 72° to T3° C, although turbidity sets in at about 60° C. 

 The presence of acetic or phosphoric acids, sodium chloride, or other 

 neutral salts, lowers the coagulation-point of serum-albumen, while the 

 presence of sodium carbonate necessitates a higher temperature. It is 

 precipitated by the strong mineral acids from its solution in dilute acids, 

 and the precipitate is readily soluble in concentrated acids ; egg-albumen 

 is not. 



2. Egg- Albumen.— In many points egg-albumen, which is contained 

 in the meshes of the fibrous net-work of birds' eggs, closely resembles 

 serum-albumen. The points of contrast are that its specific rotation is only 

 —35.5°, and when agitated with ether it is gradually precipitated. When 

 injected into a vein or the connective tissue, or when introduced in large 

 quantities into the stomach or rectum of an animal, egg-albumen is found 

 unaltered in the urine, while the injection of serum-albumen produces no 

 such albuminuria. 



A solution of comparatively-pure egg-albumen may be obtained for testing 

 by breaking the whites of several hens' eggs into a beaker, cutting up the mem- 

 branes with scissors so as to free the albumen from their meshes, stirring well 

 with an equal volume of water, and filtering through muslin. The salts may then 

 he removed by dialysis. 



Dry egg-albumen may be obtained by evaporating the above solution 

 to dryness at 40° C. So prepared, its physical properties agree closely 

 with those of serum-albumen. Its solutions have several properties which 

 enable it to be distinguished from serum-albumen. Hydrochloric acid 

 in small amount produces no precipitate ; in larger amount it causes a 

 firm coagulum, which is only with difficulty soluble in excess of acid and 

 in water and neutral salt solutions. 



3. Vegetable Albumens. — Albuminous bodies are found dissolved in 

 plant-juices and in the form of a solid in various seeds, and form the 

 most important albuminoids for the nutrition of the herbivorous domestic 

 animals. Their general properties agree with those of egg- and serum- 

 albumen, though they present certain variations among themselves in 

 composition and chemical properties. Thus, the coagulable substances 

 which may be extracted from peas and horse-beans dissolve readily in 

 lime-water and acetic acid, while the other vegetable albumens do not. 



The vegetable albumens are, as a rule, poorer in carbon but richer in 

 nitrogen than albumen of animal origin, — a fact possibly accounting for 

 their lesser nutritive value and readiness of assimilation. They usually 

 have phosphorus associated with them. Vegetable albumen is soluble in 

 cold water, and its solutions are coagulable by heat ; with dilute acids 

 and alkalies it is converted into an albuminate. In the seeds of certain 



