518 Journal of the Department of Agriculture. 



The principal facts brought forward to prove the agency of flying 

 insects in the production of this disease are: — 



(1) Blue-tongue can be produced artificially only by inocula- 



tion. All attempts to produce the divSease by drenching 

 with virulent material have failed. 



(2) By shedding and dippiug, tlie disease can be prevented by 



protectijjg the sheep from the attack of insects ; on the 

 other band, shearing sheep when the disease is prevalent 

 is apt to increase the chances of infection. 



(8) The disease is not contiacted during the day, but at night 

 time. 



(4) The disease is more prevalent in low-lying marshy districts, 

 where night insects, such as mosquitoes, are most 

 numerous, and during the season of the year when such 

 insects are most active. 



SvMJ'TOMS. 



The period of incubation varies from two to four days from 

 inoculation ; under natural conditions it is not yet determined, but is 

 probably about the same time as when produced by inoculation. 

 The temperature is high at the onset of the disease, reaching from 

 104° F. to 107° F., the fever period extending from five to seven 

 days, there being a marked drop when the eruption about the mouth 

 appears. 



One of the first symptoms noticed is a frothing from the mouth 

 and licking of the lips. If the animal is caught and examined, it 

 will be found that the mucous membrane of the moutb is inflamed, 

 showing a purplisli-blue discoloration with swelling of the gums and 

 lips. 



In very severe cases the tongue becomes badly swollen, of a dark 

 blue colour and sore from shedding of the epithelium. 



There is sometimes an (edematous swelling of the lower part of 

 the face, and of the space between the lower jaw-bones. The affected 

 animal is noticed to walk lame and tenderly, and examination of the 

 feet shows great heat and tenderness. During the febrile stage, when 

 the mouth is sore, there is great thirst, and if the affected sheep are 

 tjien allowed to drink large quantities of water, this sometimes 

 produces vomiting. 



The fatal cases usually occur amongst young animals that 

 develop sj^nptoms of diarrhtt^a and severe emaciation. 



In cases of recovery the whole course of the disease is about 

 twenty-one days. 



Post-mortem Appearances. 



As a rule, death supervenes from debility and extreme emacia- 

 tion, the lesions in the mouth in most cases have already healed, but 

 the flesh and organs are found pale and nearly bloodless. In acute 

 cases the tongue is more or less stripped of its epithelium lining, and 

 may be found gangrenous at its tip. The dental pad and inner 

 surfaces of the lips are raw and sore. The rumen often shows inflamed 

 patches. The contents of the third stomach are usually found liquid, 

 but the fourth stomach is very frequently much inflamed, in severe 



