290 PATHOGENIC BACTERIA. 



the surface, especially when the cultivation is made by 

 the method of Fernbach with, a passing current of air. 

 This mycoderma, which may appear quite regular when 

 the flask is undisturbed, is so brittle that it at once falls 

 to pieces if the flask be moved. 



Spronck has recently determined that the characteris- 

 tics of the growth of the diphtheria bacillus in bouillon, 

 as well as the amount of toxin-production, vary accord- 

 ing to the amount of glucose in the bouillon. He divides 

 the cultures into three types : 



Type A. The reaction of the bouillon becomes acid 

 and remains acid, the acidity increasing. The bacilli 

 accumulate at the bottom of the clear liquid. The 

 toxin-production is meagre. 



Type B. There is no change from alkalinity to acidity, 

 but the original alkalinity of the bouillon steadily in- 

 creases. The culture is very rich, the bottom of the 

 flask shows a considerable sediment, the liquid is cloudy, 

 and a delicate growth occupies the surface. The toxicity 

 is very great. 



Type C. In a few days the reaction of the culture 

 becomes acid, and then later on changes to alkaline. 

 During the acid period the liquid is clear, with a white 

 surface-growth. When the alkalinity returns the bouillon 

 clouds and the surface-growth increases in thickness. 

 Sediment accumulates at the bottom of the flask. The 

 toxicity of the culture is much less than in Type B. 



Spronck regards the varying reaction as due to the 

 fermentation of the glucose, and asserts that the most 

 luxuriant and toxic cultures are those in which no 

 glucose is present. To exclude as much of the undesir- 

 able sugar as possible, he makes the bouillon from the 

 stalest meat obtainable, preferring it when just about to 

 putrefy. Of the meats experimented with, beef was 

 found to be the best. 



In large cities meat is ordinarily kept sufficiently long 

 before being offered for sale to meet Spronck's require- 

 ment. 



