80 PHYSIOLOGICAL CHEMISTRY. 



logical value. The most serviceable arrangement for the study of 

 these substances, as materials of the organized fabric, should include 

 their simplest and most easily recognized physical characters, the forms 

 under which they occur in the animal frame, and the part which they 

 play in its vital operations. For this purpose they may be divided, as 

 follows, into three principal groups. 



ALBUMINOUS MATTERS. 



These are the substances which naturally stand at the head of the 

 albumenoid class. They were, many years ago, called " protein e-com- 

 pounds," because Mulder, according to a view now abandoned, consid- 

 ered them as so many combinations of the same primitive body, 

 " proteine," with varying proportions of sulphur and phosphorus. 

 They are still designated by some writers as "proteids." They are all 

 abundant ingredients of the nutritive juices, and their especial office in 

 the living body seems to be the supply of material for the nourishment 

 of the permanent structures. They include the following : 



1. Albumen of Blood. 



This substance, also called Serum-albumen or Serine, is the most 

 abundant organic ingredient of the blood-plasma, where it exists in the 

 proportion of 53 parts per thousand. After spontaneous coagulation 

 of the blood, and separation of the clot and serum, it remains fluid in 

 the serum. It is also found in the lymph, the chyle, the pericardial 

 fluid, and in many pathological serous exudations. It is obtained from 

 dilute serum by precipitating other albumen oid ingredients with acetic 

 or carbonic acid, evaporating the filtered fluid to dryness, dissolving in 

 water, and lastly removing its saline substances by the process of 

 dialysis (page 15). Serum-albumen is soluble in water and in solu- 

 tions of the neutral salts, from which it is not precipitated by either 

 dilute alkalies or organic acids. Its watery solution is neutral in re- 

 action, and rotates the plane of polarization toward the left 56. It is 

 coagulated by heat (72 C.), by the mineral acids, the metallic salts, and 

 especially by potassium ferrocyanide in acidulated solution, which is 

 the most delicate known test of its presence. It is coagulated by 

 alcohol in excess, but not by ether. Its coagula are redissolved by 

 the caustic alkalies. 



2. Egg-albumen, 



This is the main ingredient in the white of egg. It was the earliest 

 studied of all the albumenoid matters, and received its name from the 

 fact of its turning white and opaque when boiled. It is an important 

 article of food, and supplies most of the albumenoid matter for the 

 nourishment of the embryo chick during incubation. It is soluble in 

 water and in neutral saline solutions. Its specific power of rotation 

 for polarized light is 35.5. Like serum-albumen, it is coagulated by 

 heat, alcohol, mineral acids, metallic sails, and potassium ferrocyanide 

 in acidulated solution ; but it is also thrown down by agitation with 

 ether, which does not affect the preceding variety. 



