596 proceedings of section g2. 



Predisposing Causes of Braxies in General and the 

 Natural Method of Infection. 



While youth and condition are undoubtedly very important 

 factors in predisposing sheep to the disease, yet they are by no means 

 the sole or perhaps the most important. Season exerts apparently a 

 most powerful influence, but it is evident so far as the Australian 

 disease is concerned that this is only secondary. Hamilton, in the 

 group of diseases he studied, which included braxy, louping-ill, black- 

 leg, etc. , claimed a bacteriolytic substance presence in the blood during 

 that period of the year when animals are not attacked, or, as he 

 considered, " immune." His observations have not been con- 

 firmed, however, and general practice does not bear out his con- 

 clusions so far as blackleg is concerned. In my own experiments 

 no evidence of immunity has been observed at any period of the 

 year. We should seek, therefore, for additional predisposing 

 influences. So far as the European disease is concerned, I have 

 not sufficient knowledge to enable me to discuss the question 

 further than to suggest the winter incidence may be due to the 

 necessity for close grazing inducing the prehension of contaminated 

 portions of soil, and so incculation through the mouth. 



In New Zealand the " braxy-like disease " only appears, to a 

 noticeable extent at all events, in young sheep during winter 

 when feeding on turnips in the ground, and generally not until the 

 roots are eaten close to the soil. In Tasmania the earliness of the 

 spring growth seems (as recorded above) to be concomitant with 

 the appearance of the disease. In Victoria, or at any rate on 

 the property mentioned, the disease is practically confined to the 

 very dry months, and even then disappears for a time with a 

 rapid growth of grass following a summer soaking of the ground. 

 The predisposing factor of importance in each of these cases, 

 therefore, may be the 'mpossibility of the sheep avoiding the 

 ingestion of soil along with the food : in New Zealand to the 

 "shells " of the turnips adheres much soil ; in Tasmania the young 

 grass carries up a certain amount of soil in its rapid growth, as 

 does often a mushroom ; and on the Victorian property during 

 dry weather the sheep graze about the marshy places where the 

 springs debouch, and drink the water which is rendered muddy 

 by the slightest movement. Such ingestion of earth, provided it 

 be contaminated with the braxy germs, would seem to explain 

 the entrance of such an organism into the intestinal tract, and 

 also the transmission of the disease. 



But still other conditions are required. We found, for ex- 

 ample, in New Zealand that provided sheep were allowed a " run 

 off " from the turnips to rough pasturage, or were fed with straw 

 while on the turnips, that the mortahty became reduced to a 

 minimum, which seems to indicate that an empty state of the 

 stomach prior to swallowing the earth contaminated roots is a 

 necessary favourable condition. 



