332 On Certain Bacteria from the Air of New York City. 



found that only three retained the same degree of power of I'e- 

 duction, four fell back to the average of the table given above, 

 while three returned to the condition of the original culture. 

 Here we see again the marked tendency to return to the t3'pe, even 

 in this slightly differing race. These results indicate the compar- 

 ative permanency of the species and also the races of bacteria as 

 stated by Rodet to be the case. 



(2) Sports or discontinuous variations. 



In the discussion of this subject, the existence of uniform con- 

 ditions is presupposed. I consider that when the tubes are filled 

 with media from the same flask, are planted at the same time, and 

 grown on the same shelf, that these conditions are fulfilled. Or 

 even the plantings need not be made at the same time, provided 

 the conditions of temperature are approximatelj^ uniform. We 

 see cultures taken from both deep and surface colonies, from difier- 

 ent media, etc., exhibit the same characters when transferred to 

 the test media. Now if one of these suddenly exhibits different 

 characters, it is absurd to attribute the change to the action of 

 some slight, unknown and undemonstrable difference in the 

 medium or other condition. The variation is spontaneous and 

 due to the inherent properties of the germ. 



Among the Protista, one objection is always forthcoming 

 against the evidence of discontinuous variation, which does not 

 trouble us higher in the organic scale. It can alwa3's be said that 

 the variety may be a contamination, and it is almost impossible 

 to meet this objection completely. Nevertheless, I shall attempt 

 to meet it in the following instance, at least to a considerable de- 

 gree. 



In the species under investigation, Bacillus lactis erythrogenes, 

 the growth on solid media is smooth, thick and soft, uniformlj' 

 light yellow, the growth quite softly granular to the needle, not 

 in the least crusty or viscid. A culture sent to me from Krai's 

 laboratory (marked B. helvolus Zimmerman) became contaminated 

 during the summer vacation with a motile spore forming bacillus 

 (B. mesentericus vulgatus). In the process of purifying it, gelatin 

 plates were made and a culture from one of the yellow colonies 

 developed a somewhat coarsely granular growth. It was set 

 down as a contamination, although the fact that it produced a 

 slight pink tint in the medium and reacted on all the media nor- 



