484 STATE BOARD OF AGRICULTURE. 



One could perhaps conclude that the sand has practically no influence, 

 except that it prevents fast development in the drier samples. A more 

 conclusive experiment with a real pure culture could not be made for 

 lack of time. 



IV. LIFE CONDITIONS FOR ANAEROBIC MICROORGANISMS IN SOIL. 



After the previous discussions, the conditions for anaerobic develop- 

 ment can be foretold ■'.o some extent. The situation is simply that 

 changes of the moisture film will induence anaerobic and aerobic bac- 

 teria in the same way, the ellcct beinjj; entirely of physical nature, while 

 the changes due to aeration will liave the reverse effects upon anae- 

 robes. The deductions are, therefore, the following: 



1. The thicker the moisture film, the better the growth. The thick- 

 ness of the moisture film increases with grainsize and moisture content. 



2. The less aeration, the better the growth. Aeration decreases with 

 with decreasing grainsize and with increasing moisture. The differences 

 between aerobic and anaerobic organisms in soils are this : Aerobic 

 bacteria are, under all circumstances, favored by a large grainsize, be- 

 cause it increases the thickness of the moisture film as well as the 

 aeration. The moisture content, though necessary in a small degree, 

 reduces aeration very much and is by no means of unlimited benefit. 

 Anaerobic bacteria are, under all circumstances, favored by moisture, 

 because it increases the moisture film and, at the same time, reduces 

 aeration. Increase of grainsize increases the aeration faster than the 

 thickness of the film, so that one might be led to believe a small grain- 

 size most favorable. However, another feature has to be considered. 

 A thin moisture film, which is necessarily the result of a small grain- 

 size not only retards the food supply, but at the same time, favors 

 the oxygen supply. It must be kept in mind, further, that the anaerobic 

 bacteria use ]>ractical]y no oxygen at all, and therefore the ventilation, 

 or oxygen exchange, is of no importance. The oxygen present in the soil 

 is the retarding factor, its replacement is unnecessary since it does not 

 disappear. Therefore, the most im])ortant thing for anaerobic bacteria 

 is the thick moisture film, and this increases with the grainsize. Con- 

 sequently, a large grainsize is most favorable for pure cultures of 

 anaerobic bacteria. 



Alcoholic Fermentation. — An experiment illustrating this point has 

 been carried on as early as 188.^ by Soyka*. His solid medium was 

 glass beads, 0.54 mm. in diameter, his organism was Saccharoiuyccs 

 cercmsiae, his medium a sugar solution, the composition of which is 

 not given in the abstract. The yeast inoculum was varied from 5% 

 to 17% of the liquid. The fermentation was carried on for 12 hours, 

 and the results of the analysis are given as "fermented sugar in per 

 cents of total sugar." 



♦Quoted after Handbuch der Hygiene (Pettenkofer und Ziemssen) 1887. Erster^Teil, Zweite 

 Abteilung, 3 Heft: Der Boden, von Soyka; p. 227. 



