4 PHILOSOPHY OF ZOOLOGV. 



the oxygen which is required, but exercise on many spe- 

 cies a deleterious influence. To these circumstances may 

 be referred the difficulty of preserving many fishes arid 

 aquatic molhisca in glass jars or small ponds ; as a great 

 deal of the oxygen in the air contained in the water, is 

 necessarily consumed by the germination and growth of the 

 aquatic cryptogamia, and the respiration of the infusory 

 animalcula. In all cases, when the air of the atmosphere, 

 or that which the water contains, is impregnated with noxi- 

 ous particles, many individuals of a particular species, living 

 in the same district, suffer at the same time. The disease 

 which is thus at first endemic or local, may, by being con- 

 tagious, extend its ravages to other districts. 



The endemical and epidemical diseases which attack 

 horses, sheep and cows, obtain in this country the name of 

 murrain, sometimes also the distemper. The general term, 

 however, for the pestilential diseases with which these and 

 other animals are infected is Epizooty, (from mi upon, 

 and an animal. 



The ravages which have been committed among the 

 domesticated animals, at varinns timps. in Fairope, by 

 epizootics, have been detailed by a variety of authors. 

 Horses, sheep, cows, swine, poultry, fish, have all been 

 subject to such attacks; and it has frequently happen- 

 ed, that the circumstances which have produced the dis- 

 ease in one species have likewise exercised a similar in- 

 fluence over others. 



That these diseases arise from the deranged functions of 

 the respiratory organs, is rendered probable by the circum- 

 stance, that numerous individuals, and even species, are 

 affected at the same time ; and this opinion is strengthened, 

 when the rapidity with which they spread is taken into 

 consideration. 



Many diseases, which greatly contribute to shorten life, 



