THE CAUSE OF BLACK DISEASE. 11 



Experimental. 



In the previous article I dealt with the numerous inoculation experiments 

 'upon various animals, made during the investigations from 1914 to 1917, 

 with a variety of materials taken from sheep dead from black disease, and 

 also with bacteria isolated from different situations, some of which were 

 pathogenic and others non-pathogenic. Of the former, it was shown that 

 no matter how virulent the organism was on par-enteral inoculation, the value 

 of the conclusions was quite nullified unless it could be shown that the parti- 

 cular organism had been present in the body (in the strict sense of the term) 

 before death. Consequently, deductions based upon experiments made with 

 bacteria isolated from sheep "found dead," particularly anaerobes, could 

 have very little weight. 



The present account of experimental work deals with the bacillus con- 

 .sidered by the writer to be the causal organism of black disease, isolated in pure 

 culture from various necrotic foci in livers of sheep affected with that condi- 

 tion, the tissue having been removed immediately after the death of the animal. 

 To obtain such tissue, the usual procedure was followed, viz., the particular 

 flock of sheep, usually numbering two or three thousand, in which cases of 

 black disease were occurring, was closely watched and followed about the 

 paddock in which they were grazing. Immediately an animal was observed 

 sick, it was kept under closer observation for a variable period. Usually, 

 however, as soon as it was seen to be seriously ill, it was caught, placed in a 

 -vehicle or on a horse, and taken to the spot arranged for conducting thd 

 autopsies. Here again the animal was sometimes kept under observation for 

 a variable period, and at other times was killed at once. 



During the course of the field investigations, lasting about six years, sheep 

 have been killed in various stages of the disease. One has not always waited 

 until they were in extremis ; not infrequently the animal has died whilst 

 being transported from the paddock to the post-mortem shed, of ten a journey of 

 only a few minutes. Yet, although the flock had been clogely watched, the 

 animal had only a short time previously been singled out from its fellows as 

 being ill. This difficulty of picking out a sheep before it is seriously ill, from 

 a, flock of sheep kept under Australian conditions, has already been commented 

 on by the writer. 



Such specimens as were required were taken from the animal immediately 

 it had died naturally or had been killed. Rigid precautions were taken to 

 prevent contamination of the materials during the process. Instruments, 

 test-tubes, specimen bottles, &c., were all previously sterilised by the auto- 

 clave in the laboratory before leaving, because in an open paddock, no 

 matter kow -long one boiled instruments in the field, there might be a possi- 

 bility that complete sterilisation had not been effected, owing to the vessels 

 in which the sterilisation was conducted being exposed to dust, &c., during 

 boiling. This rendered one's baggage both bulky and heavy, but it had the 

 crowning merit of certainty as regards sterility of instruments, fec. 



