310 History of Animal Plagues. 



to the violence of the etFects of it. Those which are weaker from any of 

 the above causes have more aggravated symptoms, and more frequently 

 die of the disease in proportion to the degree of such causes. 



' It results, therefore, from these circumstances, that though infec- 

 tion conveyed from some beasts diseased with it is the ethcient cause of 

 the murrain in cattle, yet there is a predisponent cause, or particular 

 state of the subject, absolutely necessary to its acting or taking etfect ; 

 and this predisponent cause is the condition of the beast with respect to 

 weakness of habit or relaxation. It appears, also, that this weak state 

 of the beast may arise from general causes, either of an epidemic nature, 

 atfecting whole regions, such as inclemency of season, or scarcity of 

 wholesome food j of an endemic nature, atfecting only particular places 

 or countries, such as dampness of the air, or abundance of putrid 

 vapours j and it may be produced also from some particular cause re- 

 garding the individual only, such as original weakness of constitution, 

 pregnancy, or debility occasioned by some accidental sutfering. 



' The susceptibility to the infection, and the predisposition to be 

 more violently atfected by it, in consequence of the weakness of the 

 habit, are neither peculiar to cattle nor to this disease. It is evident, 

 from what offers in a very extensive field of observation, that both 

 mankind and brutes are liable to the attacks of most contagious dis- 

 orders in proportion to their defect of strength. Even were it not so 

 well verified by notorious facts, a theoretic proof might be drawn from 

 incontestable principles of physiology, and from the constant efi'ects of 

 medicine administered in such cases. But this is too wide a ransre of 

 subjects to be entered on here, and would, besides, requires a previous 

 acquaintance with medicinal science in order to its being understood. 

 That beasts are liable to take the infection of the murrain, and sutfer 

 more from it, in proportion to their weakness, is sutficiently obvious 

 from just remarks on the subject itself; and it is very necessary to be 

 understood and taken into consideration in all practical disquisitions on 

 that disease, because it constitutes a principle which admits two very 

 useful applications. It not only affords the means of prognosticating 

 when great numbers, or single particulars, will be seized with the disease, 

 if exposed to the contagion, and, consequently, supplies the proper 

 notice and warning for the use of preventive methods; but it furnishes, 

 likewise, the true indication of cure, and points out what tlie regimen 

 should be that will counteract the disease. 



' The manner in which the contagion may be conveyed is likewise 

 a matter of great moment in the consideration of the murrain, with a 

 view to the preventing its injurious effects. 



' The observations already made on facts have not set everything 



