338 History of Animal Plagues. 



action of the solids in giving due motion to the fluids, and from the 

 defect or perversion of the glandular secretions. In this advanced state 

 of the disease a final period is soon brought on, either by a salutary 

 crisis or the death of the beast. The morbid matter falling on some 

 particular parts, and the general depravity of the humour causing ob- 

 structions in others, topical inflammations and a general irritation follow ; 

 whence, necessarily, a fever rises in a greater or less degree. By this 

 means the force of the circulation is increased, so that, where the habit 

 is strong, the natural ferments, being again revived by the accelerated 

 motion of the fluids, prevail over that of the leaven of the contagion ; 

 and the morbid matter is either thrown on the superficial parts, in case 

 of great strength, where it forms eruptions and tumours j or discharged 

 by the glands of the intestines, in case of a less degree of strength. 

 This constitutes a salutary crisis, in consequence of which the beasts 

 recover from the murrain, at least considered as an acute disease ; though 

 they sometimes die afterwards of the ulcerations or abscesses produced 

 then by it in the brain, lungs, or other viscera. But if the natural 

 strength be so defective that the irritation and consequential fever can- 

 not produce a sufficient force of circulation to give due power to the 

 vital ferments, the contagious leaven and putrescence overcome them 5 

 and an excessive evacuation is made by the liver and the glands of the 

 small guts, which exhausts the remains of that power on which animal 

 action depends 5 while the external and weaker parts suffer a gangrene 

 from the deposit of the morbid matter, and the want of due motion of 

 the vitiated and putrid humours. 



' This investigation of the progress and manner of action of the con- 

 tagion, according to the state of the subject in the murrain, affords a 

 clear view of the indications of cure. It is evident that the strugfele 

 here betwixt health and the disease lies, in fact, at first, betwixt the 

 vital ferments which support the animal economy and a preternatural 

 ferment which tends to destroy them ; and that consequently, if the 

 latter prevail, it introduces the putrid ferment to which all animal sub- 

 stances have a disposition when it is not controlled by the vital. It is 

 certain, also, that the vital ferments depend on the due commixture 

 of the several humours and their constituent parts by the circulative 

 motion of the blood, and those other motions of the animal juices 

 which are performed by nervous action, and that these motions are 

 more or less strong in proportion to the nervous strength of the subject, 

 or, in other words, that they are rendered vigorous or languid as that 

 strength is augmented or diminished. Whatever, therefore, increases 

 this nervous strength or gives tension to the fibres, increases those mo- 

 tions, and whatever adds to the force of those motions proportionately 



