SCIENCE BULLETIN, No. 21. 



time that these bacteria were probably secondary invaders, since certain 

 hsemorrhagic areas occasionally encountered in the same organ appeared under 

 the microscope to be bacteria-free. At that period it was thought that these 

 hsemorrhagic foci were the precursors of the necrotic areas. Accumulated 

 knowledge has led me to change that opinion, and to now consider that the 

 latter are not secondary to the former, and that the hsemorrhagic foci may 

 even be due to an entirely independent cause. 



To follow the reasoning in connection with the cause of black disease, it 

 is desirable to describe more fully than previously the hepatic necrotic areas 

 met with in this condition. One or several of these lesions may be present. 

 Not infrequently they may show no surface indications of their existence, 

 their presence only being demonstrated by free incision. In view of this, it 

 is quite possible that in the early days of the investigations where no necrotic 

 lesions were recorded, such may have been present but escaped detection be- 

 cause not specifically looked for. It should be mentioned, however, that on 

 two occasions where the animal showed clinical and post-mortem signs of 

 black disease (with the exception of these liver lesions) no necrotic areas 

 could be detected after search. This feature will be referred to later and 

 a possible explanation suggested. 



The naked eye characters of the necrotic areas have already been described. 



Histology of the Necrotic Liver Focus. 



Sections show the lesion to present the appearance of coagulative necrosis. 

 It is surrounded by a broad zone of leucocytes, which sharply delimits 

 the normal from the necrotic portions. Immediately within the leucocytic 

 zone are bacilli, often in thick felted masses, arranged around the whole 

 circumference of the lesion. Many of these bacilli are of sufficient length to 

 approach that of the filamentous. Scattered among them are single vegeta- 

 tive elements, but there are no long chains of many individual rods. 

 Occasionally a sporing bacillus with a terminal or subterminal spore may be 

 seen. The bacillary rods are thick, and have rounded ends. If death has 

 elapsed a little before the removal of the affected portion of the liver, numerous 

 bacilli will be found sporing. Scattered throughout the whole of the 

 necrotic area are bacilli having the same morphology sometimes numerous, 

 at other times scanty. They are, however, usually single, and toward the 

 centre of the lesion filamentous forms are rare. Here and there rounded 

 coccus-like organisms may be seen, but these are merely the bacilli standing 

 on end in the section. The organisms are usually present in the lesions in a 

 state of purity, and they are strictly confined thereto up to the time of death, 

 for although numerous sections from the livers of various affected sheep have 

 been examined, no bacilli could be detected microscopically in the liver tissue 

 outside the leucocytic zone surrounding the area of necrosis, not even in the 

 hsemorrhagic foci, which are occasionally encountered in the same liver. 

 This absence of bacilli from all places except the area of necrosis does not 

 include those very infrequent occasions in which the animal has died from 

 clinical black disease, but there has been no naked eye evidence of focal 



