392 ACTINOMYCETES. 



granules (60, x, xi). Nevertheless virulent diphtheria 

 bacilli without granules occur, although very rarely (see 

 Kurth, /. c. ), so that a lack of the granules does not 

 exclude the diagnosis of diphtheria. (See also p. 402.) 



Relation to Oxygen. Optimum growth with entrance 

 of air ; when oxygen is excluded, the growth is lessened. 



Requirements as Regards Temperature, Reaction, 

 and Composition of the Nutrient Medium. It grows 

 well and abundantly at incubator temperature only. 

 Optimum temperature 33 to 37; extremes, about 18-20 

 and 40. Glycerin-agar is more favorable for its growth 

 than ordinary agar, but serum or ascitic nutrient medium 

 are much better. Loffler's blood-serum mixture is much 

 used (Technical Appendix) ; also Tochtermann's and 

 Deyke's nutrient media are highly recommended (Techni- 

 cal Appendix). Since we have used glycerin-ascites-agar 

 almost exclusively instead of glycerin-agar, we have 

 obtained excellent results, but one must become accus- 

 tomed to the relatively luxuriant appearance of the growth. 

 Upon gelatin at 22 24 the growth is so absolutely with- 

 out characteristics (no liquefaction), and so scanty, that 

 such cultures are never prepared. 



Gelatin Stab. Along the stab canal only a slight 

 growth. The surface growth is yellowish-white, a little 

 elevated, with a smooth wavy border and in part lobulated. 

 It is faintly shining. 



Glycerin-agar Plates. (a) Natural size: Circular or 

 roundish colonies, white to dirty yellow. The border is 

 smooth, they are more or less elevated, and with a moist 

 or faint luster. Many cultures present more luxuriant 

 (58, vii a) and many more delicate growths (58, vn ft). 



(6) Magnified sixty times : The colonies present their char- 

 acteristic form after twenty-four hours at 37. They are 

 small, roundish, usually exceedingly transparent colonies 

 of a grayish-yellow or brownish color. At the periphery 

 they are usually split or torn, and almost without excep- 

 tion are markedly crumbly. Many colonies appear at the 

 periphery as if raveled out. Still, according to the cul- 

 ture, they are thinner or thicker, lighter or darker, coarsely 

 or finely granular (59, i a and 6). After two days the 

 colonies are thicker, somewhat irregular at the periphery, 



