THE CAUSE OF BLACK DISEASE. 



normal. Not infrequently the omen turn may present numerous small haemorr- 

 hages scattered throughout its substance. The urinary bladder and urine 

 appear normal. 



It must be borne in mind that the foregoing represents the appearances at the 

 time of death. If only a few hours have elapsed between death and the holding 

 of the post-mortem examination, various changes often take place which will 

 present quite a different picture. These have been confounded with the lesions 

 of black disease (jubt as is the case with the published descriptions of the lesions 

 of hraxy in Great Britain) but must be viewed as being of purely post-mortem 

 origin. 



With the knowledge gained from the previous researches, investigations 

 were continued during 1917, 1918, and 1919, in the field and the laboratory. 

 It was evident that if the cause were bacterial and capable of being trans- 

 mitted artificially, it was not resident in any of the materials just mentioned. 

 The nature of some of the experiments showed that it wa>s not a filter passer. 

 The question then, after reviewing the subject and assuming that the cause 

 was bacterial, resolved itself into one of two possibilities, viz. : 



(1) The causal organism was confined to the lesions, whatever these 



might be. 



(2) It was confined solely to the alimentary tract. 



Experimental work eliminated the second possibility, since the feeding to 

 a number of sheep of minced up intestines, stomach, &c., produced no posi- 

 tive results, and the ascertained facts in corineccion with natural black disease 

 did not support the view that infection might be due to minute injuries to 

 the mucous membrane of the intestines. The problem was thus narrowed 

 down to the question as to whether the causal organism, if any, was only to 

 be found in the lesions. As before mentioned , the examination of animals 

 before post-mortem changes had time to set in enabled one to determine 

 which were black disease lesions and which were not. Now, although 

 bacteria could readily be detected in the congested mucosa and submucosa of 

 the abomasum and small intestines when a little time had been allowed to 

 elapse between death and the removal of the tissues, these areas were found 

 upon microscopic examination to be bacteria-free if such tissues were removed 

 and placed in a fixative solution immediately after death. The same could 

 be said of all the lesions in the various parts of Jbhe body, with the exception 

 of those portions of liver containing necrotic foci. It was very evident, 

 therefore, that if the bacteria present in such situations, with the exception 

 of the last mentioned, were the cause of death, they must primarily have 

 grown elsewhere, and that the submucosa of the stomach and intestines, the 

 kidneys, blood, &c., had only been invaded during or subsequent to the death 

 agony. Attention was, therefore, more and more focussed upon the necrotic 

 areas in the liver. It will be seen on reference to my previous article, that 

 even when these parts were removed directly death had occurred, there was 

 histological evidence of an inflammatory reaction, and that the necrotic foci 

 contained numbers of bacteria. The opinion was, however, expressed at the 



