B. DIPHTHERIA ON SERUM MIXTURE. 283- 



bouillon to which a bit of hard-boiled egg has been 

 added, the morphology of the organism is about inter- 

 mediate in both size and outline between the forms seen 

 upon glycerin-agar-agar and upon Loffler's blood-serum. 

 There will appear about an equal number of short 

 segmented and longer irregularly staining forms, but in 

 general the longest are rarely as long as the long forms 

 seen on blood-serum, and throughout they are not 

 so conspicuous for the irregularity of their staining. 



In cultures made upon two sets of nutrient agar-agar 

 tubes, differing only in the fact that one set contains 

 glycerin to the extent of 6 per cent., while the others 

 contain none, a noticeable difference in morphology 

 can usually be made out ; while the forms on the gly- 

 cerin-agar cultures are throughout small, pretty regular 

 in size, shape, and staining, those on the plain agar are 

 larger, stain more irregularly, vary more in shape, and 

 when stained by Loffler's blue are not so uniformly 

 marked by the pale transverse lines that give to them 

 the appearance of being made up of numerous short 

 segments. 



Though the outline of this organism is more regular 

 under some circumstances than others, it is nevertheless 

 always conspicuous for its manifold variations in 

 shape. 



Growth on Serum Mixture. — The medium upon 

 which it grows most rapidly and luxuriantly, and which 

 is best adapted for determining its presence in diphthe- 

 . ritic exudations is, as has been stated, the blood-serum 

 mixture of Lbffler. (See chapter on Media.) On the 

 blood-serum mixture the colonies of the bacillus diph- 

 therise grow so much more rapidly than the other 

 organisms usually present in secretions and exudations 



