1 91 9) BONAZZI—NITRIFICATIOX 203 



for the organisrrts of the Old World. Failing in the search, 

 attempts were made to iind any organism which, by its constant 

 abundance in the cultures, might prove to be the principal type. 

 On account of the slow growth of the organisms of nitrosofermen- 

 tation in the ordinary laboratory conditions, it was not until 

 nearly pure cultures were obtained that I observed, mixed with 

 and imbedded in the salt deposit, a large coccus form, much 

 resembling the one described by Wixogradsky as peculiar to 

 South American soils. The strong ''ferment power" of this 

 organism had aided it in escaping attention in impure cultures. 

 These megalococci are shown in fig. 6. They are large. ^i.2^ix 

 in diameter, and of a slightly irregular roundish form. Some 

 are occasionally found which appear to have a triangular section, 

 but closer observation reveals them to be clumps of smaller cells 

 arranged so as to simulate a tetrahedron. 



The microscopical examination of material from cultures in 

 full nitrification, answering to the criterion of purity, is the most 

 instructive. Fig. 5 shows the appearance of the megalococci at 

 this time; they are composed of a thick gelatinous mass in which 

 are imbedded small granules. Very often seemingly bipolated 

 bodies are imbedded in this jelly, but on closer examination these 

 polar bodies appear to be, not small cocci, but diplococci, the true 

 living active units (figs. 4, 5). Material from intensive cultures, 

 observed fresh in strong Meissner solution, showed these struc- 

 tures very plainly stained differentially and larger than in the 

 dried preparations, since on drying the gelatinous mass seems to 

 lose its thick structure. This gelatinous coat has a thickness 

 that equals the diameter of the cells imbedded in it, and it takes 

 on a bluish tinge in iodine, while the imbedded cells stain golden 



'es 



yellow in the same reagent. 



When the cultures are in full and strong nitrification, the 

 megalococci give rise to the small cocci which we will name /?. 

 The latter are clearly shown in fig. 5. These small (3 forms, which 

 were at first imbedded in a thick gelatinous mass, forming the 

 large a cocci, are set free and begin independent life, leaving the 

 empty sheaths which are occasionally to be seen in stained prepa- 

 rations. Some of the jS forms have been observed to take up a 



