140 LECTURES ON 



in sugar is more rapid. The oils in the pure state, as well as the 

 organic acids, are extremely slow in alteration. The albuminoids, 

 also, when dry may be kept at ordinary temperatures for an indefinite 

 time with no symptoms of change. If, however, they be exposed to 

 warm air in the moist state, they speedily undergo the process of 

 putrefaction; they decay with great rapidity, and with the production 

 of volatile bodies having a most intense and noisome odor. 



The albuminoids are highly complex in their chemical composition; 

 their atoms are, so to speak, delicately poised, and in a condition 

 of unstable equilibrium, and, for this reason, liable to easy disturbance 

 by any external agency. Hence, they at once break up into several 

 less complex and more stable compounds when heat and oxygen act 

 upon them with the intervention of water. Not only so, but in their 

 fall they entangle the carbo-hydrates, the oils, the acids, and in fact 

 all the organic constituents of the plant. In this way the soluble 

 albuminoids act as ferments. Sugar dissolved in water is slow to 

 change, until a decaying albuminoid, furnished by yeast, be added, 

 Avhen it is rapidly transformed into alcohol or acetic acid and carbonic 

 acid. Butter, if carefully made, keeps sweet a long time ; but if the 

 casein of the milk be not thoroughly removed, it speedily becomes 

 rancid, when air and warmth act upon it. 



It is possible that the carbo-hydrates, if they could be absolutely 

 separated and protected from matter containing nitrogen, would be 

 found capable of perpetual preservation, even in contact with water, 

 for in the presence of a minute quantity of some metallic salt, or other 

 body that makes insoluble (inactive) compounds with the albuminoids, 

 they do remain unaffected for long periods. Thus wood, which, though 

 chiefly consisting of cellulose or other non-nitrogenous bodies, is not 

 free from albumin, when exposed to the weather — i. e., to oxygen, 

 water, and warmth — undergoes that form of slow decay known as 

 mouldering or humifaction, the immediate visible result of which is 

 vegetable mould or humus. If, however, the wood be first saturated 

 with corrosive sublimate (kyanized) or blue vitrol, it resists decay for 

 a long time. 



As it happens naturally, with very few exceptions, the organic 

 matter of vegetation, or of animals that have subsisted upon and 

 been formed from vegetation, falling upon the surface of the earth or 

 buried a little way beneath it, find just the conditions of decay; and 

 their nitrogenized ingredients yielding first to the sway of oxygen, 

 involve with them the whole organism, so that nothing but their 

 mineral matters, which are already oxyds, escape the destruction. 



The process of decay, thus sketched in outline, includes, however, 

 numberless intermediate stages. Thus wood in its decay yields a 

 large series of bodies which have the collective name of humus, but 

 are distinguished into several groups, as the humic acids, ulmic acids, 

 and geic acids, the latter comprising crenic and apocrenic acids. These 

 bodies all differ from wood, out of which they originated, by containing 

 much less hydrogen and oxygen compared to carbon. We can, in fact, 

 trace the gradual removal of these elements up to a certain point, after 

 which other products arise from the simple oxydation of those first 



