THE CAUSE OF BLACK DISEASE. 13 



recorded. Subsequent inoculation experiments with sheep that had been 

 drenched with cultures, indicate that the administration of virulent material 

 by way of the alimentary tract confers little or no immunity. 

 Subcutaneous and Intramuscular Inoculation. Small doses up to 0-25 c.c. 

 produce in the sheep considerable local and systemic disturbance, but are not 

 always fatal. The latter amount will frequently kill, but the result is not 

 constant. Doses of from O5 to 1'5 c.c. of culture are almost invariably fatal 

 to sheep of any age in from about twenty-eight to seventy-eight hours, usually 

 in less than forty-eight hours. Sheep that survive experimental infection for 

 three days often recover. With subcutaneous inoculation there is, about 

 .fifteen hours afterwards, considerable swelling around the site of injection, 

 which gradually extends, at first mainly in a downward direction (gravita- 

 tion). If the injection be into a limb, the swelling gradually reaches the 

 coronet. As the condition progresses pronounced lameness appears, the 

 animal often carrying the affected leg. The swollen part in the early stage 

 of the disease is oedematous, and pits readily on pressure ; later on it becomes 

 firmer. There is no noticeable gas formation. For a while the skin itself 

 shows no sign of change, but about twenty-four hours after the injection a 

 small livid spot appears at the point of entrance of the needle. The lividity 

 gradually spreads, its actual extent appearing to depend upon how long the 

 .animal survives. If death occurs in about forty hours, it may be only about 

 half an inch or stf in diameter. If the animal lives longer, the area may extend 

 several inches around the needle puncture. In cases where a slightly attenu- 

 ated culture (artificially attenuated) has been employed, and the animal has 

 survived, a very pronounced livid area of varying extent appears at the 

 inoculation site, succeeded by necrosis of the overlying skin. 



There is a moderate hyperthermia (about 105 deg. Fah.), with the usual 

 clinical manifestations of profound systemic disturbance. Later, the animal 

 becomes very quiet, and readily permits ifaelf to be handled, or may even 

 refuse to move. At this period, however, the mental faculties do not appear 

 to be impaired. In the final stages the animal becomes comatose and dies 

 very quietly. 



Post-mortem Appearances. If the autopsy has been made immediately 

 .after death, the most striking changes are observable in the inoculated area. 

 In the case of injection into the thigh, the wool is easily pulled out of that 

 limb. An oedematous swelling extends downwards to the coronet and 

 upward.-, to the groin. At times, however, the upward extension of the 

 swelling is absent, At others, the upward extension, instead of gradually 

 diminishing, terminates abruptly. Possibly this is the effect of gravity on 

 the contained exudate. 



As already remarked, there is a larger or smaller area of lividity around 

 the point of inoculation. If death has ensued soon after the injection, this 

 area may be minute. If the animal has survived two days or so, the sub- 

 cutaneous tissue in the inoculation area is considerably thickened, and shows 

 evidence of necrosis. The subcutaneous tissues of the swollen part are 

 .saturated with an odourless exudate, which, near the inoculation site, is often 



