648 PATHOGENIC MICROORGANISMS 



Winslow, Kligler and Rothberg, 6 on the basis of recent careful invests 

 gations, describe the typhoid bacillus as a Gram-negative, non-spore 

 forming, actively motile rod which forms translucent irregular colonies 

 on gelatin, and a colorless growth on potato. It produced strong and 

 prompt acid, but no gas, on media containing the hexoses, maltose, 

 mannit, sorbit, xylose (rapid or slow), and dextrin; it does not attack 

 arabinose, rhamnose, or lactose; produces a slight initial reddening of 

 litmus milk, which, after two weeks, reverts to neutrality or slight alka- 

 linity. It does not form indol, nor liquefy gelatin, does not grow in 

 asparagin-mannitol medium, does not reduce neutral red, and causes 

 browning of lead acetate medium (irregular) . It has low tolerance for 

 acid, but high tolerance for malachite and brilliant green dyes. It has 

 characteristic serum agglutination. 



Differences Within the Typhoid Group. Recent work has shown 

 that not all typhoid bacilli are culturally alike, there being two distinct 

 groups, one which ferments xylose rapidly, the other slowly. Since 

 there are also antigenic differences it may be necessary in the future 

 to speak rather of a typhoid group than of the typhoid bacillus. 



Xylose fermentations of typhoid bacilli have recently been studied 

 in more detail by Krumwiede, Kohn and Valentine, 7 and by Morishima. 8 

 The first-named authors inoculated 37 strains of typhoid bacilli into 

 xylose broth and found that 29 of them produced acid within twenty- 

 four hours, while 8 of the strains required from five to thirteen days for 

 this result. Morishima, of this "laboratory, obtained rapid and slow 

 xylose fermenters from a single strain by repeatedly fishing different 

 colonies on plates. An atypical strain has recently been described by 

 Bull and Pritchett 9 whose bacillus agglutinated in typhoid serum typ- 

 ically up to 1 to 20,000, but which gave positive indol reactions. 



Biological Considerations. The typhoid bacillus is an aerobic and 

 facultatively anaerobic organism growing well both in the presence and 

 in the absence of oxygen when certain sugars are present, showing a 

 slight preference, however, for well aerated conditions. It grows most 

 luxuriantly at temperatures about 37.5 C., but continues to grow within 

 a range of temperature lying between 15 and 41 C. Its thermal death 

 point, according to Sternberg, is 56 C. in ten minutes. It remains alive 

 in artificial cultures for several months or even years if moisture is sup- 

 plied. In carefully sealed agar tubes Hiss found the organisms alive 

 after thirteen years. In natural waters it may remain alive as long 



7 Krumwiede, Kohn and Valentine, Jour, of Med. Res., 38, 1918, 89. 



8 Morishima, Jour, of Bacter., March, 1921. 



9 Bull and Pritchett, Jour, of Exper. Med., 24, 1916, 55. 



