THE CAUSE OF BLACK DISEASE. 



necrosis in the liver. Yet bacilli having the characters of black disease 

 bacilli have been isolated from that organ. It will be seen later that it is 

 considered that these eases are ones of mass infection, the animal dying 

 before a gross lesion has had time to develop. 



It is quite probable that invasion of the surrounding liver tissue from a 

 -necrotic focus and thence of the blood vessels, in conjunction with bacteria 

 from the intestines may take place very soon after death. The histology of 

 the lesion and the disposition of the bacilli recall that of bacterial necrosis of 

 the liver, much more common in cattle, however, than in sheep, due to the 

 necrosis bacillus, although the morphology of the two organisms differs very 

 considerably. In my former article, in order to guard against arriving at 

 conclusions without sufficient evidence, it was stated that the mere presence 

 of organisms in a lesion is not in itself sufficient to prove that those particular 

 organisms are the cause of death of the animal in which they may be found, 

 -or that they are the cause of the disease under investigation. When, however, 

 in animals affected with a particular disease, certain lesions are of very 

 common if not invariable occurrence in an organ, and when in such lesions 

 there are constantly found bacilli apparently in pure culture, further 

 investigations are indicated as to the role they play. When portions of an 

 organ containing si^ch lesions are removed immediately after death in an 

 aseptic manner, and placed at once in a fixative solution, the probability of 

 post-mortem invasion of such tissues by bacteria is negligible. Furthermore, 

 in addition to the necrotic lesions containing the particular organism in large 

 .numbers, there is also distinct evidence of reaction on the part of the tissues 

 to the bacterial invasion, and the bacilli in the cases just mentioned, as far 

 as has been ascertained, are confined to these necrotic foci. 



All the foregoing factors enumerated, taken collectively, should afford 

 satisfactory evidence that the bacteria in question were present in the 

 situations where they have been demonstrated, some time before death 

 occurred. They, therefore, are clearly not agonal invaders. 



The question to be decided is whether the r61e they play in black disease 

 is the primary, or only a secondary one ? In my former article, I remarked 

 that they were apparently secondary invaders, because they were absent from 

 the hsemorrhagic hepatic foci which one occasionally met with, and because 

 inoculation experiments on a guinea-pig and a rabbit were negative. It was 

 at that time thought by the writer that these hsemorrhagic areas were the 

 precursors of the necrotic lesions. This, as before remarked, I now consider 

 in. all probability to be an error ; the former may have quite an independent 

 origin, e.g., early acute fluke infestation, or perhaps they are due to the toxin 

 produced by the causal bacteria. For the failure to infect a rabbit and a 

 guinea-pig with cultures of organisms isolated from a necrotic liver focus in 

 Case 14, described in the before mentioned article, several explanations 

 present themselves ; e.g., the bacillus may have become attenuated by various 

 means during the laboratory manipulation, especially by cultivation in 

 glucose media, not much particular attention being paid to the preservation 

 of virulence, as the organism" at that time was thought to be a secondary 



