A ferment which has finished its work, replied Pasteur, and which for want of aliment cannot continue it, becomes in its turn an accumulation, so to speak, of dead organic matters. Such, for example, would be an accumulation of yeast exposed to the air. Leave this mass to itself in summer temperature, and you will see appear in the interior of the mass anaérobic vibrios and the putrefactions associated with their life when protected from contact with the air. At the same time, on the surface of the entire mass--that is to say, that which finds itself in immediate contact with the oxygen of the air--the germs of bacteria, the seeds of mould will grow, and, by fixing the oxygen, determine the slow combustions which gasify the mass. The ferments of ferments are simply ferments. As long as the aérobic ferments of the surface have at their disposal free oxygen, they will multiply and continue their work of destruction. The anaérobic vibrios perish for want of new matter to decompose, and they form, in their turn, a mass of organic matter which, by and by, becomes the prey of aérobies. The portion of the aérobies which has lived becomes the prey either of new aérobies of different species, or of individuals of their own species, so that from putrefaction to putrefaction, and from combustion to combustion, the organic mass with which we started finds itself reduced to an assemblage of anaérobic and aérobic germs--of those same germs which were mixed up in the original primitive organic substances. Though a collection of germs becomes again in its turn a collection of organic matter, subject to the double action of the phenomena of putrefaction and of combustion, there need be no anxiety as to their ultimate destruction; in the final analysis they represent life under its eternal form, for life is the germ, and the germ is life. * * * * *