SOIL 
695 
of the elements wliich enter into its composition— ammonia, carbon 
dioxide, hydro<j;en sulphide, and so on— and those which transform 
these simple compounds, especially annnonium salts, into nitrites and 
eventually into fully-oxidized (mineralized) nitrates. In the latter 
form the nitrogen originally present in organic matter is available for 
plant synthesis into protein through the action of sunlight upon the 
chlorophyll of the vegetable kindgom, thus completing the cycle. 
The initial phase in the degradation of dead organic matter to 
ammonium salts and simple compounds of the other elements which 
comprise the protein molecule appears to be accomplished largely 
through the activity of bacteria of the Subtilis-]Mesentericus and 
Proteus Groups. These organisms elaborate powerful active soluble 
proteolytic enzymes which liquefy protein, and eventually the intra- 
cellular digestion of the hydrolytic cleavage products of protein by 
these microorganisms results in ammonia formation. ^ 
Fig. 103. — Bacillus siihtilis showing spores. X 1000. 
The Proteus Group has been discussed elsewhere.- The cultural 
characters of the Subtilis-^Iesentericus Group are as follows: 
Morphology.— Rod-shaped organisms with rounded ends, occurring 
usually in chains of greater or lesser length. The individual cells 
measure from 0.7 to 1.2 microns in diameter, and vary in length from 
2.5 to 9 microns. The members of the group are actively motile prior 
to sporulation and possess numerous peritrichic flagella. No capsules 
are formed, but spore formation is a characteristic feature of the group. 
The morphological details of spore formation and spore germination 
are relied upon largely to distinguish the various members f)f the 
group, but these details are of no practical significance in this dis- 
cussion.'' 
' Kendall, Day and Walker: Jour. Am. Chcm. Soc, 191.3, 35, 124.3; ibid., 1914, 
36, 1966; Jour. Infee. Dis., November, 1915. 
2 Page 394. 
3 Gottheil: Centralbl. f. Bakteriol., 1901, 7, Abt. II. Arthur Meyer: Practicum d. 
botanischen Bakterienkunde, Jena, 1903. Chester: Delaware Coll. Agr. Exp. Sta. 
Ann. Rep., 1902-1903. 
