CHAPTEE IV. 



ALBUMINOUS MATTEES. 



THE proximate principles belonging to this class are very important, 

 not only from their peculiar physiological properties, but also from 

 their comparatively abundant quantity in the animal body. They are 

 derived both from animal and vegetable sources. But in plants, as a 

 general rule, the albuminous matters, though constantly present, and 

 essential to the activity of vegetative life, are in small quantity as com- 

 pared with other ingredients of the fully developed tissues. In man and 

 animals, on the other hand, they constitute by far the larger part of all 

 the solid constituents of the body. Everywhere their chemical consti- 

 tution, their physical characters, and the distinctive properties which 

 belong to them, show that they have an intimate connection with the 

 more active phenomena of living beings. 



The first peculiarity by which they are distinguished from the proxi- 

 mate principles of the preceding class, is that they contain nitrogen, in 

 addition to the three elements belonging to other organic bodies, namely, 

 carbon, hydrogen, and oxygen. They are, therefore, sometimes called 

 the "nitrogenous" proximate principles. But, as we shall hereafter 

 see, there are various other substances, of a crystallizable nature, also 

 containing nitrogen, which are produced in the body, and which are of a 

 different character from the albuminous matters. 



The albuminous matters are not crystallizable. They always, when 

 pure, assume an amorphous condition, in which they are sometimes 

 solid, as in the bones ; sometimes fluid, as in the plasma of the blood ; 

 and sometimes semi-solid in consistency, or midway between the solid 

 and fluid condition, as in the muscles and the substance of the 

 glandular organs. Even in the fluids, the albuminous matters, when 

 present in considerable quantity, as in the blood-plasma, the pancreatic 

 juice, or the subrnaxillary saliva, give to the solution a peculiar 

 viscid or mucilaginous consistency. This consistency is more marked, 

 in proportion to the abundance of the organic ingredients. The 

 albuminous matters, in solution, all rotate the plane of polarization 

 toward the left. The precise chemical constitution of these substances 

 has not been in all cases determined. The apparent variation in the 

 exact proportion of their ultimate elements in different instances is 

 probably due to the readiness with which they become modified in the 

 processes of nutrition, many of them passing into each other under the 

 influence of digestion and assimilation. There are, no doubt, a great 

 variety of these matters existing in the body, only a certain number of 



