BACTERIAL CONTENT OF THE SOIL 137 



Bacillus ethaceticus, cultivated from sheep-dung by P. FRANKLAND, J. Fox (I.), 

 and MACGREGOR (I.). This is a motile rod about 0.8-1.0 /u. broad and 1.5-5.1 /* 

 long, which, however, seems to lack the faculty of producing spores. It fer- 

 ments glycerin, mannite, and arabinose in such a manner that the chief 

 products are, in addition to small quantities of formic acid and succinic acid, 

 ethyl alcohol and acetic acid, the ratio found being, in the first instance 

 2. 1 1 : i ; in the case of mannite, 1.63 : i ; and in the last, i : 1.96. In a 

 subsequent communication FRANKLAND and FREW (I.) demonstrated that glyceric 

 acid, CH,.OH CH.OH COOH, is decomposed in the same way, the molecular 

 ratio of the ethyl alcohol to the acetic acid being about i to 4. 



Whereas the last-named bacillus leaves dulcite unattacked, this hexavalent 

 isomer of mannite is fermented by Bacillus ethacetosuccinicus. This microbe was 

 discovered by P. FRANKLAND and W. FREW (II.) in a solution of ammonio-ferric 

 citrate, which, originally intended for photographic purposes, was found to 

 have spontaneously fermented with vigour. These observers give the following 

 equation as a deduction from their experiments : 



3C 6 H 14 6 = 4C 2 H 6 + 2CH 2 2 + C 2 H 4 2 + C 4 H 6 4 + 2C0 2 + 2H 2 . 

 Dulcite, Ethyl Formic Acetic Succiuic Carbon Hydro- 



Mannite. alcohol. acid. acid. acid. dioxide. gen. 



Many other bacteria also produce ethyl alcohol, but only one more will be 

 noticed, and that a pathogenic organism, viz., Friedliinder's Bacillus pneumonice. 

 According to the researches of F. BRIEGER (I.), and of P. FRANKLAND, STANLEY, 

 and FREW (I.), this bacillus, when grown in nutrient solutions containing sugar 

 (saccharose, glucose, mannite), produces ethyl alcohol and acetic acid, together 

 with other fermentation products in smaller amount. These four examples may 

 suffice to support the assertion made above, that ethyl alcohol is producible by 

 bacterial activity. No practical application of this is made in the arts, the 

 higher fungi known as "yeasts" being exclusively used; consequently this 

 property of many Schizomycetes will not be referred to again. We will now 

 supplement the account given of the hay- and potato-bacilli by a few remarks on 

 the 



112. Bacterial Content of the Soil. 



To determine this quantitatively the procedure followed is to finely divide a 

 weighed quantity of soil in sterilised water and then prepare cultures from the 

 washings in the usual manner. P. MIQUEL (IV.), to whom we are indebted for 

 the first determinations made in this connection, fixed the unit of weight to be 

 taken as one gram, and it is to this unit that all the subjoined data refer. 



It would, from the first, be expected that layers of the same soil at different 

 depths would exhibit differences, both quantitatively and qualitatively, with 

 regard to their bacterial inhabitants. The property of soils (especially clays) of 

 combining with the fertilising materials supplied in manures, prevents these 

 substances from penetrating in any quantity to great depths, and from this 

 circumstance alone one would expect the number of bacteria in the subsoil, at 

 considerable depths below the surface, to be but small. The filtering action of 

 the upper layers of the soil also conduces to the same end, these layers fixing not 

 only the fertilising substances, but also (and that in a purely mechanical way) 

 the bacteria applied to the soil in manures. Thus it happens that subsoil water 

 is perfectly free from, or at least very poor in, bacteria ; a fact established 

 by PASTEUR and JOUBERT (I.), and of which C. FRAENKEL (III.) has given 

 instructive examples. (A remarkable exception to this rule was reported by 

 S. ROHN and H. WICHMANN (I.)-) Finally, the influence of aeration should not 

 be forgotten. Thip, in the lower and comparatively undisturbed layers, is almost 



