104 JOHNKS DISEASE 



in which the essential substance is not mixed well with 

 the egg. These elevated colonies are well shown in 

 Plate IX., Figs, i and 2. When streak subcultures 

 are made on to the same media with a platinum loop, 

 growth occurs along the needle track. The growth in 

 this case does not greatly differ from that obtained in 

 primary cultures, except that it is more rapid, and the 

 colonies usually coalesce to form a continuous irregu- 

 larly heaped-up growth. This is shown on a tube of 

 medium that contains the chloroform insoluble portion 

 of a cooled and filtered alcoholic extract of B. phlei, 

 and is illustrated in Plate VI., Fig. i. If, in place of the 

 saline in the medium one uses peptone-beef broth, the 

 growth is certainly more vigorous ; this is illustrated 

 in Plate IX., Fig. 3. If the broth is made from brain, 

 such as sheep's brain, the improvement is still more 

 marked (see Plate VII., Fig. i). In this case the growth 

 cannot be distinguished from that of a vigorous-growing 

 culture of the human tubercle bacillus on ordinary 

 Dorset's egg medium (see Plate VII., Fig. 2), and is more 

 copious than that of either the bovine or the avian 

 tubercle bacillus grown on Dorset's egg medium. A 

 culture of the avian type of bacillus grown on egg 

 medium is shown in Plate VII., Fig. 3. If, in these 

 media, the egg is replaced by blood-serum or ascitic 

 fluid, Johne's bacillus does not grow so well. 



Agar Media containing the Essential Substance. — 

 When the essential substance or a bacillus containing 

 the essential substance is added to glycerine-peptone- 

 beef broth-agar, the growth of Johne's bacillus is slower 

 and not so vigorous. The growth, however, does not 

 greatly differ from that which occurs on the egg media, 

 except that it is usually more coloured. The agar 

 medium, however, is improved by the addition of 

 blood-serum, or ascitic or pleuritic fluid, and growths 



