THE VOLATILE PABT OF PLANTS. 109 



therefore designated by Liebig as the plastic elements of 

 nutrition. They have also been termed the blood-build- 

 ing or muscle-forming elements. It is, in all cases, the 

 plant which originally constructs these substances, and 

 places them at the disposal of the animal. 



The albuminoids are mostly capable of existing in the 

 liquid or soluble state, and thus admit of distribution 

 throughout the entire animal body, as in blood, etc. They 

 likewise readily assume the solid condition, thus becom- 

 ing more permanent parts of the living organism, as well 

 as capable of indefinite preservation for food in the seeds 

 and other edible parts of plants. 



Complexity of Constitution. — The albuminoids are 

 highly complex in their chemical constitution. This fact 

 is shown as well by the multiplicity of substances which 

 may be produced from them by destructive and decom- 

 posing processes as by the ease with which they are 

 broken up into other and simpler compounds. Kept in 

 the dissolved or moist state, exposed to warm air, they 

 speedily decompose or putrefy, yielding a large variety of 

 products. Heated with acids, alkalies, and oxidizing 

 agents, they mostly give origin to the same or to anal- 

 ogous products, among which no less than twenty differ- 

 ent compounds have been distinguished. 



The numbers of atoms that are associated in the mole- 

 cules of the proteids are very great, though not in most 

 cases even approximately known. The HaemogloMn of 

 blood, which forms red crystals that admit of preparing 

 in a state of great purity, contains in 100 parts — 



The iron (Fe) is a constant and essential ingredient, and 

 if one atom only of this metal exist in the haemoglobin 

 molecule, its empirical formula must be something like 

 C64oHioooN"io4FeS20i9o, and its molecular weight over 14,- 

 000. Haemoglobin readily breaks up into a proteid and a 



