168 JOHNKS DISEASE 



substance. They are collected, centrifuged, and 

 washed, and six drops are added to one drop of a 

 homogeneous emulsion of the bacillus to be tested, 

 together with two drops of a normal guinea-pig's serum, 

 and the mixtures are incubated at 37° C. In every 

 case, if the emulsion be not too thick, phagocytosis is 

 complete in about twenty-four hours. The comparative 

 non-toxicity of Johne's bacillus for the leucocytes is 

 shown by the fact that the remaining tubes containing 

 human, bovine, or avian tubercle bacilli, or B. phlei^ 

 soon become contaminated, showing death of the leuco- 

 cytes ; while the tube containing Johne's bacillus re- 

 mains sterile for a longer time, and the leucocytes 

 appear normal. On the other hand, these are partially 

 degenerated in the tube containing B. phlei, and are 

 completely so in those containing tubercle bacilli. 



From what has been said above it is clear that 

 Johne's bacillus has a low degree of toxicity, especially 

 for such animals as rabbits. As we have seen, in 

 cattle that suffer naturally from Johne's disease toxic 

 symptoms are very little in evidence, and the tempera- 

 ture remains constant throughout, showing a lack of 

 any general disturbance of the animal economy, whilst 

 the absence of local necrosis seems to indicate that the 

 bacillus has no very harmful influence on the neigh- 

 bouring cells. The rise of temperature sometimes 

 met with in very advanced cases is probably due to a 

 secondary infection with intestinal micro-organisms 

 the general resistance of the animal being low owing 

 to malnutrition. In some cases the number of bacilli 

 found on post-mortem examination is small, and from 

 this certain authors have assumed that the symptoms 

 accompanying the later stages of the disease are 

 directly caused by highly toxic substances secreted by 

 the bacilli. The view, however, generally held is 



