THE CAUSE OF BLACK DISEASE. 17 



before removal. Owners have informed me that no cases occur in a subse- 

 quent season in a clean paddock (that is, paddocks in which black disease 

 has never been known to occur) to which an affected flock has beem 

 removed, but of this latter I have no direct evidence. All the evidence 

 goes to show that the causal organism of black disease is a facultative 

 parasite, and that the places most dangerous for sheep are the springs and 

 moist, undrained areas in the paddocks. The disease appears peculiar to 

 the sheep, for other animals grazing over the same country remain un- 

 affected. Popular opinion considers that the springs and moist places are- 

 the localities whence the disease arises, although the view is that it is due 

 to eating plants growing therein, e.g., watercress. Fluke disease of the 

 liver is very common among all sheep in the area in which black disease 

 is known to occur. Some sheepowners have observed the coincident 

 occurrence of black disease and fluke infestation. This has led a few of 

 them to express the opinion that the former is nothing else but acute fluke- 

 disease of the liver. That this is not the case is shown by the fact that 

 fluke disease is common in numerous parts of New South Wales and else- 

 where, but black disease or anything resembling it is unknown in many 

 such places. 



Experimental. It has been demonstrated that the administration of 

 large amounts of virulent sporing bacilli by the alimentary tract fails to- 

 set up any sign of infection. Consequently the mere ingestion of con- 

 taminated water or food can hardly be considered to be the usual method 

 of natural infection. The same deduction may be drawn from the feeding 

 experiments made with minced organs and viscera, &c., from animals dead 

 from natural infection. The subcutaneous inoculation of small amounts of 

 culture are very fatal to susceptible animals, and always gives rise to 

 definite changes at and around the site of inoculation. Mere scarification 

 is insufficient to infect. Seeing that in naturally-occurring cases no 

 cutaneous or muscular lesion is encountered in animals examined imme- 

 diately they are dead (if one excepts the occasional presence of a clear 

 intermuscular or subcutaneous exudate in certain situations), it is quite 

 reasonable to conclude that the common natural method of infection is not 

 through the skin. The same reasoning may be advanced against the view 

 that the bacilli gain entrance to the body by means of small abrasions of 

 the mucosa of the alimentary tract, including the abomasum. Infection 

 by inhalation may be dismissed as the least probable method of any. 



Another important feature of the disease is that of the hepatic lesion or 

 lesions. If this is, as I consider it to be, the primary lesion in black 

 disease, the question at once arises, how does it originate? The writer 

 has made post-mortem examinations 011 many hundreds of sheep at various 

 times and places, but has not seen these particular hepatic lesions in any 

 condition other than black disease, although focal necrosis of the liver may 

 be caused by other agents. Seeing that experimentally-ingested bacilli fail 

 to infect, one naturally seeks an explanation as to the means whereby th 

 bacilli reach the liver and produce the special lesions therein. After 

 t 38219 B 



