614 president's address. 



a parallel case in the plague bacillus as affecting m<m and the 

 rat in common, the latter being, like the rabbit, a rodent. 

 There is also the question whether the means proposed are 

 likely to have the desired effect. While thousands of rats 

 have died through the operation of plague, in no case do we 

 hear that there has been extermination. The disease only kills 

 those individuals which are susceptible, leaving the others 

 which are sufficiently resistant to recover or to escape infection 

 altogether; and when the epidemic has, as it is termed, "run 

 its course," the balance of population is quickly restored from 

 the surviving immune stock. There appears to be no reason to 

 expect anything else with rabbits; it seems inevitable that there 

 will be no extermination, but merely a killing off of susceptible 

 individuals, leaving the others to propagate, while we have the 

 serious risk that the disease will not confine itself to the rabbit, 

 for there is no foretelling in what direction it may develop or 

 what other animals may be attacked when the bacillus has become 

 acclimatised. That some microbic diseases are prof oundly altered 

 in their nature by passing through one or more hosts of different 

 species, is now well established, and there is no guarantee that this 

 rabbit disease — which we are informed is not directly communic- 

 able to man — may not become so after affecting another animal^ 

 which may, perhaps, be reptile, mammal or bird. The same 

 danger applies to domestic animals and stock, which may quite 

 possibly become secondar}'- hosts for^ the bacillus. Bacteriology 

 has taught us in how remarkable a manner many bacilli are able 

 to adapt themselves to new conditions, and how readily and 

 unexpectedly they will become acclimatised when their surround- 

 ings are altered. 



There appears to be a good deal of mystery about the precise 

 nature of the disease which it is proposed to utilise, and different 

 statements on this point have found currency. As bearing on 

 the whole question, it may not be out of place to mention a fact 

 which does not appear to be very well known in Australia, that 

 in certain parts of Europe a disease known as rabl)it syphilis is 

 prevalent amongst these creatures, and though, so far as is known, 



