12 MASS. EXPERIMENT STATION BULLETIN 319 



In order to detect variants among any strain of bacteria, it is necessary to 

 establish a criterion for a so-called "normal" or typical strain. Rettger (1900) 

 first described the organism as a Gram-negative, actively motile, non-liquefying, 

 non-chromogenic, facultatively anaerobic bacillus with slightly rounded ends. 

 When grown on agar the bacilli vary in size from 0.3 — 0.5 micron in breadth and 

 from one to two microns in length. On agar plates the colonies are small (one- 

 fifth of a millimeter) and white after twenty-four hours of incubation, but they 

 may attain a diameter of one millimeter after several days of incubation. The 

 colonies vary in form from oval, kidney-shaped, or even spindle-shaped, to round. 

 In almost every case the colony surface is marked by a peculiar rosette figure. 



Rettger and Harvey in 1908, after a more extensive study of the disease, con- 

 cluded that the organism is a long, slender bacillus (.3-.5 X 1-2.5 microns) with 

 slightly rounded ends. It usually occurs single, chains of more than two bacilli 

 being rarely found. It is Gram-negative and stains readily by the ordinary basic 

 anilin dyes. It is non-motile, non-liquefying, non-chromogenic, non-sporogenic, 

 and facultatively anaerobic. On agar plates the colonies appear white and small 

 at the end of twenty-four hours. They increase in size slowly and seldom attain 

 more than one millimeter in diameter, even after a few days incubation. Under 

 the microscope they appear yellow and vary in shape from oval and spindle- 

 shaped to round. A rosette surface is usually demonstrable. On slant agar the 

 growth resembled that of the typhoid bacillus. 



Rettger and Plastridge (1932) in their recent monograph on pullorum disease 

 state that in heavily seeded meat extract slants or plates the colonies are discrete 

 and appear more or less dewdrop-like. When isolated on meat infusion or liver 

 infusion agar the growth is more luxuriant, with characteristics approaching those 

 of the coli-typhi group. Rosette figures are usually present on the colony surface. 



In the examination of primary isolations the author accepted the afore- 

 mentioned characteristics as a criterion for normal or typical S. pullorum. How- 

 ever, among the strains investigated it was observed that certain characteristic 

 features may be added to those described above. On plain meat extract agar 

 (pH 7.0 — 7.2) heavily seeded with inoculum, the colonies appear discrete, smooth, 

 glistening, homogeneous, entire, dome-shaped, transparent, and varying in form 

 from round to angular. On chicken infusion agar the growth is slightly more lux- 

 uriant, with colonies possessing a lesser degree of transparency. On liver infusion 

 agar the growth is even more luxuriant than on meat infusion medium. The colo- 

 nies are smooth, round, entire, glistening, homogeneous, markedly translucent, 

 and extremely dome-shaped. Congested colonies remain small (1 mm. or less), 

 but isolated colonies may attain a diameter of three to four millimeters or more. 

 Surface markings may appear as the colony increases in size and age, but as a rule 

 the young colony on a heavily seeded plate changes little with age. 



The cellular morphology of the organisms taken from growth on meat extract 

 agar resembled closely the description cited above. In most smears an occasional 

 filament and large cell was observed. Similar observations were made in smears 

 prepared from growth on meat infusion agar. However, a most striking picture 

 was noted in smears prepared from colonies on liver infusion agar. The cells were 

 considerably larger, stained with different degrees of intensity, and varied quite 

 markedly in their shapes. This cellular response will be discussed further in 

 another section. 



In the fermentative studies the following substances were employed to identify 

 5. pullorum: dextrose, maltose, lactose, sucrose, and dulcitol. The production 

 of acid and gas or acid only in dextrose was considered typical of the organism. 



Antigens were prepared by removing the growth from young cultures with 0.9 



