Generic Characters in the Coccaceae 



189 



or more of the 10 tubes, while 48 cuUures formed nitrites alone, and 53 

 cultures ammonia alone, according to the same standard. It seems 

 improbable that in the latter case nitrites had been formed and 

 entirely reduced to ammonia. We are inclined rather to conclude 



TABLE 31. 

 Correlation between Nitrite Formation and Ammonia Formation. 



that two different types of reduction exist, in one of which ammonia 

 is produced directly. 



As regards correlation with other properties, we have seen that 

 the production of nitrites, and still more notably that of ammonia, 

 is especially characteristic of the cocci isolated from the air. It 

 is, of course, possible that this may be indirectly connected with 

 the fact that forms which have survived drying and dispersal through 

 the air must be particularly well adapted to conditions which obtain 

 in the nitrate solution. A similar law is apparently manifest in the 

 striking relation to vigor of surface growth. The power of forming 

 both reduction products increases progressively with the richness 

 of surface growth, being entirely absent in the "very faint" class. 

 No relation appears between nitrate reduction and optimum tem- 

 perature, and the only other correlation to be considered is that 

 with gelatin liquefaction shown in Table 32. 



TABLE 32. 



Correlation between Nitrate Reduction and Gelatin Liquefaction. 



Table 32 shows the usual large proportion of organisms which 

 do not exert nitrate reduction, but it may be noticed that some 30 

 per cent of the liquefiers reduce nitrates, against only 20 per cent 

 of the non-liqucficrs. Again, only 6 per cent of the non-liqueticrs, 

 against 16 per cent of the liquefiers, form ammonia. 



