12 MICROBES AND TOXINS 



and that our digestion is accompanied by a commencement of 

 putrefaction, and of intoxication. The aerobic bacteria of 

 the Proteus group can produce putrefaction there, but it is 

 chiefly the anaerobes, as was Pasteur's opinion, which do this. 

 There have been found in the human intestine all the most 

 important of these, the B. putrificus, the B. sporogenes, and 

 the B. perfringens. The anaerobic flora of the intestine does 

 not differ much from the anaerobic flora of the putrefying meat 

 in Tissier's experiments. These microbes produce poisons 

 which are the true source of auto-intoxications (Metchnikoff). 

 For life in general, putrefaction is necesssary to permit of the 

 circulation of nitrogen in nature : but our own particular 

 interest demands that putrefaction should not begin too soon, 

 i.e., in our intestine, and mask itself under an appearance of 

 perfect health. 



To combat the intestinal putrefaction, it is necessary to 

 adopt a diet capable of producing in us that limit of acidity 

 which induces the crisis separating the two phases of putre- 

 faction of meat or milk, and of arresting decomposition in our 

 bodies at the end of the first phase. Therefore, we ought to 

 eat carbohydrates and sugars, and so alter the conditions 

 in our intestine as to favour the lactic ferments. 



IV. Nitrification and Denitrification. 



Nitrates represent the form of nitrogen preferred by the 

 plants, and it has long been known that the ammonia set free 

 in putrefaction becomes oxidised in the soil, the ammonium 

 salts being transformed into nitrates. This is the process 

 of nitrification and is carried on by bacteria. 



It was long thought that the ammoniacal salts were oxidised 

 in contact with the soil by the direct action of atmospheric 

 oxygen, in the same way that certain chemical combinations 

 can take place on contact with porous substances. But chalk 

 and sand, which ought to act as porous substances, cannot 

 take the place of earth. Pasteur perceived with his peculiar 

 intuition that the lower plant must play a part in nitrification. 



