Treatment of ijrass Land for EUnnnation of Disease. 77 



from the contaminated pastures removes the immediate danger, 

 and prolonged absence leads to elimination of this form of con- 

 tamination, and as this worm does not infest animals of other 

 species, such may be grazed in the polluted situation without 

 fear. This removal of the seed-bed is often the only practicable 

 measure at our disposal for the elimination of diseases from 

 grass land. 



It would probably be incorrect to assume that, apart from 

 their existence in animals, disease-producing organisms are 

 u])iquitous or permanent residents on grass land ; but it must 

 be recognised that its disease-producing quality depends on its 

 pollution with disease germs emanating from animals. These 

 may be deposited directly by animals on to pasture, or be brought 

 thither with food, manure, or other contaminated material. 

 The degree and extent of contamination and the danger to 

 animals grazing on them will materially depend on whether 

 the seeds of disease are sparsely or profusely discharged 

 during life by infested or infected animals — conditions applic- 

 able to the spread of disease generally. Take for contrasting 

 examples anthrax and foot-and-mouth disease ; in case of the 

 former there is practically no discharge of the causal bacilli 

 during life, or, at any rate, while the subject is moving about, 

 and the number of animals dying at each outbreak averages 

 less than two, the extensive fatalities which occasionally 

 result from improper disposal of carcasses, &c., being included 

 in the computation. In case of the latter, in which discharge 

 of virus is profuse, if unrestrained, perhaps GO to 80 per cent, 

 of animals grazing with the affected one would contract the 

 malady. These diseases may also be used to exemplify the 

 varying periods during which grass land may remain contamin- 

 ated. It has been stated that anthrax spores may retain their 

 vitality in the outer world for years ; it may be mentioned 

 that in dealing with the outbreaks of foot-and-mouth disease 

 which have occurred in Great Britain for many years, animals 

 have been allowed to go on to pastures in which the affected 

 had been grazing in about a month or six weeks after the 

 existence of the disease had ])een reported, as far as we can 

 discover, without recurrence in the same place. 



The adoption of measures for the elimination of disease 

 from grass land must be considered with the view of preventing 

 its pollution, and destroying the organisms of which that 

 pollution consists. In seeking for the sources of pollution it 

 is essential to bear in mind that harmful parasites of various 

 kinds are much more frequently than is ordinarily supposed 

 resident, usually in small numbers, in apparently healthy 

 animals, and these or their germs are discharged on to many 

 pastures on which grazing animals remain unaffected by 



