552 Professor David James Hamilton [March 8, 



the fact that Braxy occurs almost exclusively in one-year-old 

 animals, it would seem that by some means nature renders the 

 animal immune to the disease during its first year of existence, 

 and, manifestly, if we could imitate the means adopted by nature 

 we might have every hope of saving the lives of a large number 

 of animals which otherwise would be doomed. It is evidently 

 those animals which have not been rendered immune before the 

 advent of the Braxy season which fall victims to the disease, and 

 hence all the more reason why we should endeavour to forestall 

 nature and insure that this much-to-be-envied condition of immunity 

 is established in every instance l)efore the susceptible period com- 

 mences. The same line of argument holds good of the other 

 diseases of the class. 



How to bring about this condition of immunity is accordingly the 

 prime factor to be considered by way of treatment. The favourite 

 means in practice, in the case of other contagious diseases, is that of 

 injecting subcutaneously some of the blood-serum obtained from an 

 animal rendered artificially immune. The serum taken from the 

 immune animal has the property of conferring immunity on the fresh 

 host. This method, however, is impracticable in sheep-farming 

 operations. It would require an enormous amount of immune serum 

 to satisfy the demands of even a limited district, and, besides, it 

 necessitates the use of a subcutaneous injection syringe, an instrument 

 constantly liable to go wrong in unskilled hands. 



Then there is the method of injecting the organism subcutaneously 

 which is the cause of the disease, but this again requires the use of a 

 subcutaneous syringe, and, besides, is most uncertain and dangerous 

 in its application. 



What has proved in my experience the most practicable and 

 successful method is that of administration of the organism by the 

 mouth. Nature evidently brings about immunisation by the organ- 

 ism being taken up from the pasture, passing into the stomach and 

 intestine, fructifying in these organs, and throwing off a poison 

 which, getting into the blood, has the effect of acting upon it and 

 rendering the animal proof against an attack of the natural disease. 



Now, it is evident that this means of protecting the animal might 

 quite well be imitated artificially, and that, if practised at a season 

 when the diseases in question do not prevail, might be employed with 

 little risk of killing the animal by communicating a fatal attack of 

 the malady. Such is the system I have been pursuing for the last 

 two years, and, as time goes on and I am getting more experience 

 from the experiments which are being made, I feel justified in ex- 

 pressing the conviction that we are at least on the right track. It 

 must, however, be clearly understood that all our trials of the system 

 as yet are purely experimental. The lay mind, and especially the 

 sheep-farmer mind, is inclined to regard all such investigations from 

 a hard-and-fast point of view, (juite oblivious of the fact that sub- 



