PRINCIPLES OF VETERINARY SURGERY 147 



the watery anilins. Loeffler's solution will stain it in the tis- 

 sues. 



Pathogenicity. — The bacillus will produce the disease in 

 young cattle, between the ages of six months and four years. 

 Older animals are seldom attacked. It may also affect sheep 

 and goats, but horses, dogs and hogs are immune. The dis- 

 ease is strictly a wound disease. The microbe is introduced 

 into the subcutem, where it produces an advancing 

 oedematous and emphysematous swelling at the seat of en- 

 trance, together with grave systemic disturbances that prove 

 fatal in several days. The bacillus gains admission through 

 insect bites, punctures, abrasions, etc. 



Resistance. — The spores may be preserved indefinitely 

 in a dry environment, and cold as low as 98° Fahr. below 

 zero has failed to kill it (Law). It is killed by boiling for 

 twenty minutes, but the spores resist boiling for six hours. 

 It is killed quite readily with the ordinary chemical antisep- 

 tics, mercuric chloride, carbolic acid, sulphate of copper, and 

 boracic acid. In the soil, if sheltered from the atmosphere, 

 it will live indefinitely. 



Immunity. — Immunity may be acquired by vaccination. 

 The blackleg vaccine is prepared from the dried and pulver- 

 ized muscles of calves that have been artifically infected. 

 When the calf dies the infected muscles are taken out, cut 

 into pieces and dried slowly at about the heat of the body. 

 When dried it is pulverized and the living bacteria are at- 

 tenuated with heat of about 212'' Fahr. or slightly higher for 

 six or seven hours. The resulting product is the first vac- 

 cine. The second vaccine is submitted to but 185° Fahr. 

 These two vaccines are injected subcutaneously at an inter- 

 val of one week. More recently, however, it has been found 

 that a safe immunity may be obtained from a single inocula- 

 tion with a virus submitted to 185° for six or seven hours. 

 The vaccination is not entirely without the danger of produc- 



