18 PHYSIOLOGICAL CHEMISTRY. 



in the eggs of certain fishes and amphibians does not consist of 

 pure albumin, but of an albumin containing large amounts of 

 lecithin which seems to be combined with mineral substances. 

 Crystalline combinations of albumin with mineral substances have 

 been prepared from seeds of various plants, and lately crystallized 

 animal albumin in combination with salts has been prepared 

 (HOFMEISTEK). In the dry condition the albuminious bodies ap- 

 pear as a white powder, or when in thin layers as yellowish, hard, 

 transparent plates. A few are soluble in water, others only soluble 

 in salty or faintly alkaline, or acid solutions while others are insol- 

 uble in these solvents. All albuminous bodies when burnt leave 

 an ash, and it is therefore questionable whether there exists an al- 

 buminous body which is soluble in water without the aid of mineral 

 substances. Nevertheless it has not been thus far successfully 

 proved that a native albuminous body can be prepared perfectly 

 free from mineral substances without changing its constitution or 

 its properties. The albuminous bodies are in most cases strong 

 colloids. They diffuse, if at all, only very slightly through animal 

 membranes or parchment-paper, and the albumins have generally 

 a very high osmotic equivalent. All albuminous bodies are optically 

 active and turn the ray of polarized light to the left. 



On heating a solution of albumin to the temperatures depending 

 on the albumin present, and with the proper reactions and in 

 favorable external conditions, as, for example, in the presence of 

 neutral salts, most albuminous bodies separate in the solid state as 

 a crude or " coagulated " albumin. The different temperatures at 

 which the various albuminous bodies coagulate in neutral, salty 

 solutions give in many cases a good means for detecting and sepa- 

 rating these bodies. 



The general reactions for the albuminous bodies are numerous, 

 but only the most important will be given here. To facilitate the 

 study of these they have been divided into the two following groups. 



A. Precipitation Reactions of the Albuminous Bodies. 



1. Coagulation Test. An alkaline albumin solution does not co- 

 agulate on boiling, a neutral solution only partly and incompletely, 

 and the reaction must therefore be acid for coagulation. The 



