8 MASS. EXPERIMENT STATION BULLETIN 319 



standpoint of the organism and tests employed. 



Savage and White (1925) stated that in direct platings from pathological 

 material, colonies of Salmonella bacilli and other intestinal pathogens were, as 

 a rule, wholly smooth. Occasionally, however, roughness might be detected in 

 the primary cultures. They demonstrated in a few experiments that "rough" 

 forms possess a lower pathogenic and invasive power than the smooth type. 

 Also, they inferred that in nature a process of natural selection tending to smooth- 

 ness doubtless occurs, but that this presumably consists in the weeding out of 

 "rough" variants which may have low pathogenicity and penetrating power. 

 They suggested maintaining smooth cultures either by animal passage or by 

 using unheated culture medium. 



In 1925 Enderlein described in great detail the phenomenon of cyclogeny. 

 He defined cyclogeny of bacteria as a cycle of morphological development com- 

 mencing with the simplest morphological unit, "mychit", passing through the 

 highest morphological structure, and then returning to the "mychit" stage. 

 The different stages of morphological structure were designated as cyclostages, 

 and a single passage through a cyclogenic development process was called a 

 cyclode, which had a peak in its development that was designated as "Kulmina- 

 tion". Virulence and pathogenicity were associated with the parasitic cyclostage, 

 which was the virostage. 



Jordan (1926) demonstrated that single cell strains of paratyphoid bacilli of 

 the "R" and "S" types could more or less regularly be made to yield cells of the 

 opposite type by appropriate treatment. 



White (1926) called attention to the effect of alcohol on rough variants. Rough 

 forms were extracted with 96 per cent alcohol, which conferred upon the most 

 salt-sensitive strains a degree of suspension stability at least equal to that of the 

 normal smooth races. Among the 21 rough strains examined in the various 

 Salmonella types, he did not encounter an exception or partial exception to this 

 rule. Agglutination tests were performed satisfactorily with 0.85 per cent NaCl, 

 and even at twice this concentration. 



In 1927 Webster and Pritchett reported that smooth colony types of para- 

 tvphoid-enteritidis bacilli prevailed throughout the various stages of rodent 

 typhoid infection. In the same year Webster and Burn reported the effects of 

 external conditions in the occurrence of smooth, mucoid, and rough colony types 

 in Bad. enteritidis. 



Goyle (1927) was successful in deriving two forms (N and R) from Bad. typhosum 

 and Bad. enteritidis by plating old broth cultures. The colonies of the "R" form 

 differed from those of the "N" form in being larger and in having a surface which 

 was markedly granular. An "S" form was obtained by growing the "N" type on 

 phenol-agar, but it did not remain as a permanent variant. He observed that the 

 "N", "S", and "R" forms differed in their antigenic, absorbing, and agglutinating 

 properties. 



In 1927 Arkwright reported that variants may be distinguished by a great 

 variety of characters, some of which vary quite independently, while others are 

 closely linked or correlated. Virulence of a culture and its value as a prophylactic 

 agent may often be foretold, without animal inoculation, from purely cultural 

 or cultural and serological features. He found that vaccines prepared from "R" 

 forms gave comparatively slight protection, while "S" forms made efficient 

 vaccines. 



In 1927 Gwatkin reported the isolation of a weak pullorum phage from an 

 abscess in a rabbit inoculated with Bad. pullorum. Pullorum cultures placed in 

 contact with this phage yielded two types of colonies. The individual bacteria 



