434 Diphtheria 



growth of the bacillus usually occurs; but upon the third, scattered 



cream-white colonies suitable for transplantation can usually be 



found. 



: The studies of Michel* have shown that the development of 



the culture is much more luxuriant and rapid when horses' serum 



instead of beef or calves' serum is used. 



Westbrook suggested that the addition of a small amount of 

 glycerin to the preparation of blood-serum would prevent it from 

 drying so rapidly as usual and would have the added advantage of 

 preventing the growth of certain varieties of bacteria not desired. 

 Dubois t carried out a series of observations upon this question 

 and found that 3 to 5 per cent, of glycerin makes a very valuable 

 addition, as the diphtheria bacilli grow very rapidly and almost 

 in pure culture upon the blood-serum mixture to which it is added. 

 The blood-serum is not liquefied or otherwise visibly changed! 



Potato. — Upon potato it develops only when the reaction is 

 alkaline. The potato growth is not characteristic. 



Milk. — Milk is an excellent medium for the cultivation of Bacillus 

 diphtheriae. The milk is not coagulated. Litmus milk is useful 

 for detecting the changes of reaction brought about. Alkalinity, 

 which at first favors the development of the bacillus, is soon replaced 

 by acidity that checks it. When the culture bgcbmes old, the reac- 

 tion may again become strongly alkaline. .This variation in reac- 

 tion seems to depend entirely on the transformation of sugar in the 

 media. 



Vital Resistance. — As the diphtheria bacillus does not form spores, 

 it possesses very little vital resistance and is delicate in its thermic 

 sensitivity. It grows slowly at 2o°C., rapidly at 37°C., and ceases 

 to grow at about 4o°C. It is killed when exposed to 58°C! for a 

 few minutes. Besson states that when dried in fragments of false 

 membrane it resists high temperatures and has been found alive 

 after exposure to ioo°C. for an hour. Drying quickly destroys it, 

 but if organic matter be present it may remain alive a long time. 

 Roux and Yersin were. able to keep the bacilli alive in a piece of dry 

 pseudo-membrane, kept in the dark, for five months. 



Reyes has demonstrated that in absolutely dry air diphtheria 

 bacilli die in a few hours. Under ordinary conditions their vitality, 

 when dried on paper, silk, etc., continues for but a few da^ys, though 

 sometimes they can live for several weeks. In sand exposed to a 

 dry atmosphere the bacilli die in five days in the light; in sixteen 

 to eighteen days in the dark. When the sand is exposed to a moist 

 atmosphere, the duration of their vitality is doubled. In fine 

 earth they remained alive seventy-five to one hundred and five 

 days in dry air, and one hundred and twenty days in moist air. 



* " Centralbl. f . Bakt. u. Parasitenk.," Sept. 24, 1897, Bd. xxn, Nos. 10 and 11 

 t "Seventeenth Annual Report of the Department of Health and Charities," 

 Indianapolis, Ind., 1907. 



