CHAPTER I 



THE GENERAL FUNCTIONS OF MICROBES — THE TRANSFORMATION 

 CYCLES OF CARBON AND NITROGEN 



The circulation of matter ; anabolism and catabolism — Views of Lavoisier — 

 The transformation cycles of carbon and nitrogen — The role of micro- 

 organisms : I. Maturation of the soil and formation of arable land. 

 II. Fermentation of vegetable matter — Decomposition of starch and 

 manure— Hypotheses on the formation of coal. III. Putrefaction of 

 albuminous materials. IV. Nitrification and denitrification : in agricul- 

 ture ; in the biological purification of sewage. V. Fixation of atmos- 

 pheric nitrogen in the soil : by bacteria alone ; by bacteria in 

 association with algse ; by the nodule bacteria of Leguminosse — 

 Some ideas about the useful micro-organisms : Fermentations in con- 

 nection with food production and in various industries. 



Almost all living matter is made up of water, that is to say, 

 of oxygen and hydrogen, and of compounds of carbon and 

 nitrogen. Other elements may enter into the tissues of 

 animals and vegetables, for example, sulphur, iron, arsenic, 

 boron ; but by following the circulation of carbon and 

 nitrogen, it is possible to have a general view of the movements 

 of exchange between matter and life. 



The living creature restores to nature what it has absorbed, 

 and eventually its own body, by its excretions during life and by 

 its decomposition after death. The elements set free are 

 recombined into organic bodies, and these exchanges and this 

 circulation form the essence of life. It is an abuse of our 

 subjective attitude to consider as two opposites life and death. 

 At most, life is the opposite of inertia. Death is a special kind 

 of accident, life being the all-embracing phenomenon. The 

 first of the work ers in the great cycle of life are the microbes, 



