THE NITROGENOUS BODIES 79 



THE NITROGENOUS BODIES. 



Nitrogenous bodies take the chief part in forming the solid tissues of the 

 body, and are found also to a considerable extent in the circulating fluids 

 (blood, lymph, chyle), the secretions and excretions. They often contain, 

 in addition to carbon, hydrogen, nitrogen, and oxygen, the elements sulphur 

 and phosphorus; but although the composition of most of them is approxi- 

 mately known, no general rational formula can at present be given for the 

 proteids. 



Proteids. The nitrogenous substances constitute the most im- 

 portant and complex compounds of the body. According to their chemi- 

 cal composition and reactions they are divided into three main classes, viz., 

 i, simple proteids; 2, compound proteids; and 3, albuminoids. 



The proteids are the chief of the nitrogenous organic compounds and 

 exist in both plants and animals, one or more of them entering as an essential 

 part into the formation of all living tissue. They exist abundantly in the 

 lymph, chyle, and blood. Very little is known with any certainty about 

 their exact chemical composition. Their formulae are unknown, the chem- 

 ists who have attempted to construct the structural formulae differing very 

 greatly among themselves. In fact the very term proteid is an extremely 

 arbitrary one. It simply means a body which, according to Hoppe-Seyler r 

 contains in its molecule the elements carbon, hydrogen, nitrogen, oxygen, 

 and sulphur, in certain arbitrary but varying amounts, thus Carbon, from 

 51.5 to 54.5; Hydrogen, from 6.9 to 7.3; Nitrogen, from 15.2 to 17; Oxy- 

 gen, from 20.9 to 23.5; Sulphur, from 0.3 to 2. Some proteids contain from 

 0.8 to 4.5 per cent of phosphorus; a small amount of iron is usually associ- 

 ated with proteids, but it is not certain whether or not it is an integral part 

 of the molecule. Chittenden defines a proteid as a substance which con- 

 tains carbon, hydrogen, oxygen, nitrogen, and sulphur, the nitrogen being 

 in a form which serves the physiological needs of the body; and yields, on 

 decomposition, a row of crystalline amido-acids and crystalline nitrogenous 

 bases; nearly all contain 52 per cent of carbon and 16 per cent of nitrogen. 



Properties of Proteids. Proteids are for the most part amorph- 

 ous and non-crystallizable. Certain of the vegetable proteids have been 

 crystallized, and according to Hofmeister, egg albumin is also capable of 

 crystallization. They possess as a rule no power (or scarcely any) of passing 

 through animal membranes. They are soluble, but undergo alteration in 

 composition in strong acids and alkalies; some are soluble in water, others 

 in neutral saline solutions, some in dilute acids and alkalies, none in alcohol 

 or ether. Their solutions exercise a left-handed rotation on polarized light. 



The hope that it may be possible in the immediate future to synthesize 

 proteids is not very great, because of the extraordinary variety of compounds 

 obtained by the decomposition of proteids by various chemical methods, 



