124 MICROBES, FEKMENTS, AND MOULDS. 



both in air and water may, therefore, be indefinitely 

 preserved in a protective medium, such as a brick 

 wall covered with plaster. They are nourished at 

 the expense of the ammoniacal salts which are found 

 in the air in a gaseous state, and which are fixed by 

 atmospheric moisture, and it is probable that they 

 derive little nutriment from the solid materials in 

 the midst of which they live, although by their 

 increase disintegration may ensue. Hence, especially 

 from the hygienic point of view, it is so important to 

 disinfect the walls of hospitals, barracks, stables, etc., 

 by scraping and whitewashing them. 



Parize also believes that microbes may perform 

 a geological part in nature by disintegrating the 

 schistoid rocks which enter into the constitution of 

 arable soil. But we are now speaking of microbes of 

 recent origin, since the temperature to which clay is 

 subjected in order to make red bricks would certainly 

 destroy all the microbes and their germs. This is not 

 the case with the microbes of chalk, which, according 

 to Be'champ, are of very ancient origin. 



XIII. THE MICROBES OF CHALK AND COAL. 



Be'champ's researches tend to show that microbes, 

 which he calls microzyma, or small ferments, have an 

 almost indefinite term of life. We know that chalk 

 consists almost entirely of the remains of the calcareous 



