26 



of the original, and all the other characters were true. Upon plating, 

 some colonies gave rise to the original soft smooth growth ; a series 

 of cultures made after exposing the variety for varying lengths^ of 

 time to the sunlight also showed one tube like the original, a tube 

 made after 30 minutes' exposure. This result is explicable on the 

 theory of the selective action of sunlight, as noted below. 



Variations in colony contour, noted in the case of B. ruber 

 indicus, B. rutilus, B. fuchsinus, B. amyloruber, and 

 rarely for B. kiliensis, where proteus-like and round surface 

 colonies appeared on the same plate, are to be explained partly 

 through physical conditions of the media, and partly by spontaneous 

 variations which arise in the viscidity of the capsular envelope or 

 in the motility of the organism. Agar streaks from the proteus 

 colonies were sometimes slightly more spreading, but the next plate 

 might show total reversion to the round type. 



B. plymoutheusis is recorded in the original description as 

 differing from B. prodigiosus in marked viscosity on agar and 

 potato cultures. Dyar (loc. cit.) uses viscidity of B. plymouthen- 

 s i s to distinguish it from B. prodigiosus and B. rosaceus 

 metalloides. My culture also differed in producing gas in lactose 

 and sucrose bouillon and in standard asparagin dextrose solution, 

 as well as in a strong fecal odor. During a two years' obser- 

 vation of this culture, viscosity seemed as constant a character of 

 B. plymouthensis as any other of these differences. But the 

 next year, upon revival of the cultures after two months' summer 

 storage, B. prodigiosus I was found to evince the agar culture 

 viscosity of B. plymouthensis. Contamination naturally suggested 

 itself as first explanation, but plating and examination showed the 

 prodigiosus culture to be true in all other respects as noted 

 above, and it was necessary to ascribe the viscosity to a variation 

 which had arisen in the old summer culture and become dominant 

 accidentally in the first plating. Three different cultures now show 

 this peculiarity, the third, B. prodigiosus VIII, presenting it when 

 received at the laboratory. These observations make it necessary 

 to drop the character of viscosity or capsule formation as differen- 

 tial for B. plymouthensis. 



In general, what we are in the habit of regarding as important 

 biological characters are not subject to sudden or spontaneous vari- 

 ation; i. e M the power of liquefying gelatin, of producing gas, or 

 of coagulating milk, does not appear or disappear abruptly with no 

 apparent cause. As has been observed in varieties appearing in the 

 same culture of B. coli 1 ), the variants are chiefly due to a 

 morphological change, such as the production of more or less of the 

 capsular substance upon which often depends the configuration of 

 surface colonies, or to change in an easily disturbed physiological 

 character such as excretion of pigment. 



1) Smith, T., and Reagh, A. L. The agglutination affinities of rela- 

 ted bacteria parasitic in different hosts. (Journ. ofMed. Research, Vol. IX. 1903, 

 p. 270.) 



