VARIATION OF SALMONELLA PULLORUM 5 



Goodman (1908), by artificial selection, obtained a strain of C. diphtheriae 

 which had moderate power of producing acid in dextrose broth, and two strains 

 possessing respectively a greatly augmented and greatly diminished power of 

 acid production. He suggested that fermentative properties are not species 

 characters, since the zymogenic power exhibited can be readily and markedly 

 altered at will by artificial selection. 



Buchanan and Truax (1910) attempted to select high and low acid races of 

 Strept. lacticus, but found no evidence of a divergence of high and low races among 

 the cultures studied. They concluded that impressed variations did not appear 

 to be heritable and that continued growth of Strept. lacticus under favorable 

 conditions, seemed to render the organism less variable. 



Jacobsen (1910) isolated a typhoid strain which he designated typhoid mutabile, 

 since it was characterized by a restricted colony type possessing slight agglutina- 

 bility and yielding secondary colonies which resembled typical typhoid in mor- 

 phology and serological behavior. 



Burri (1910) encountered an organism belonging to the coli-typhoid group 

 which he designated Bad. imperfectum, since it was unable to ferment saccharose, 

 but, when cultivated in the presence of this carbohydrate, certain colonies acquired 

 this property. The latter he named Bad. perfectum. Since the ability to ferment 

 saccharose was acquired gradually, he concluded that this property appeared to 

 be latent in the imperfectum type. 



Typhoid strains could be trained to attack dulcitol, according to Penfold 

 (1911). Non-fermenting colonies on dulcitol agar plates revealed after five days 

 or more secondary colonies as papillae which might or might not possess an acid 

 reaction. He further observed that Bad. typhosum could be trained to ferment 

 lactose only with very great difficulty, and that the newly acquired property 

 was very unstable and transient. He concluded that papillae formation indicates 

 that variation affects only very few individuals of a colony to a great extent, and 

 does not guarantee permanency in the character. 



Rettger and Sherrick (1911) stated that bacterial variation may be brought 

 about by artificial selection. They maintained that variation does not depend 

 solely upon changes in nutriment, environmental conditions, etc., but that it is 

 frequently brought about through inherent properties within the organism itself. 

 By artificial selection they obtained from a slightly pigmented strain of B. pro- 

 digiosus two strains showing in one case brilliant coloration and in the other 

 complete absence of color. Also, they observed the return of the pigment-pro- 

 ducing property in a strain of Ps. pyocyanea which had previously been very 

 nearly colorless. 



Miiller (1911), working with typhoid and known pseudo-dysentery bacteria, 

 observed secondary colonies when growing these organisms on rhamnose agar. 

 He regarded this as a new characteristic comparable to that of Bacterium coli 

 mutabile, and further observed the same forms on old gelatin cultures of typhoid. 



Dobell (1912) concluded that bacteria are subject to mutation in that a given 

 race may give rise to a new race which differs from the parent strain in its genetic 

 make-up. The new characters of the race may be transmitted for many genera- 

 tions. 



Revis (1912) subjected a typical strain of Bad. coli to peptone broth which 

 contained malachite green. Subsequent culture on ordinary agar yielded large, 

 viscous, circular masses, which consisted of a mixture of very long filaments and 

 short bacilli, together with a gummy cementing substance. He found this strain 

 to differ physiologically, morphologically and culturally from the typical Bad. 

 coli. 



