Book II. ANIMAL PATHOLOGY. ^^^ 



Chap. V. 

 Animal Pathology ; or the Duration, Diseases, and Casualties of Animal Life. 



1990. Each species of animal is destined, in the absence of disease and accidents, to 

 enjoy existence dunng a particidar period. In no species, however, is this term absolutely 

 limited, as we find some individuals outliving others, by a considerable fraction of their 

 whole lifetime. In order to find the ordinary duration of life of any species, therefore, 

 we must take the average of the lives of a number of individuals, and rest satisfied with' 

 the approximation to truth which can thus be obtained. There is little resemblance in 

 respect of longevity between the different classes, or even species, of animals. There is no 

 peculiar structure, by which long-lived species may be distinguished from those that are 

 short-lived. Many species whose structure is complicated live but for a few years, as 

 the rabbit ; while some of the testaceous Mollusca, with more simple organisation, have 

 a more extended existence. If longevity is not influenced by structure, neither is it 

 modified by the size of the species. While the horse, greatly larger than the dog, lives 

 to twice its age, man enjoys an existence three times longer than the former. 



1991. Tiie circumstances which regulate the term of existence in different species ex- 

 hibit so many peculiarities, corresponding to each, that it is difficult to offer any general 

 observations on the subject. Health is precarious, and the origin of diseases generally 

 involved in obscux-ity. The condition of the organs of respiration and digestion, 

 however, appears so intimately connected with the comfortable continuance of life, and 

 the attainment of old age, that existence may be said to depend on the due exercise of 

 the functions which they perform. Whether animals have their blood aerated by means 

 of lungs or gills, they require a regular supply of oxygen gas : but as this gas is exten- 

 sively consumed in the process of combustion, putrefaction, vegetation, and respiration, 

 there is occasionally a deficiency in particular places for the supply of animal life. lu 

 general, where there is a deficiency of oxygen, there is also a quantity of carbonic acid or 

 carburetted hydrogen present. These gases not only injure the system by occupying the 

 place of the oxygen which is required, but exercise on many species a deleterious influ- 

 ence. I'o these circumstances may be referred the difficulty of preserving many fishes 

 and aquatic Mollusca 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 noxious 

 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. 



1992. The endemical and epidemical diseases which attack horses, sheep, and cows, obtain in this 

 country the name of murrain, sometimes also that oithe distemper. The general term, however, for the 

 pestilential diseases with which these and other animals are infected, is Epizboty {epi, amongst, xoon, 

 an animal). 



1993. The ravages which have beeti committed among the domesttca/ed animals, at various times, in 

 Europe, by epizbbties, 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 happened, that the circumstances which 

 have produced the disease in one species have likewise exercised a similar influence over others. That 

 these diseases arise from the deranged functions of the respiratory organs, is rendered probable by the 

 circumstance 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. 



1994. Many diseases, which greatly contribute to shorten life, take their rise from circum.stances con- 

 nected with the organs of digestion. Noxious food is frequently consumed by mistake, particularly by 

 domesticated animals. When cows, which have been confined to the house during the winter season, 

 and fed with straw, are turned out to the pastures in the spring, they eat indiscriminately every plant 

 presented to them, and frequently fall victims to their imprudence. It is otherwise with animals in a 

 wild state, whose instincts guard them from the common noxious substances of their ordinary situation. 

 The shortening of life, in consequence of the derangement of the digestive organs, is chiefly produced by 

 a scarcity of food. When the supply is not sufficient to nourish the body, it becomes. lean, the fat being 

 absorbed to supply the deficiency ; feebleness is speedily exhibited, the cutaneous and intestinal animals 

 rapidly multiply, and, in conjunction, accelerate the downfal of the system. 



1 995. Jlie power of fasting, or of surviving without food, possessed by some animals, 

 is astonishingly great. An eagle has been known to live five weeks without food ; a 

 badger a month ; a dog thirty- six days ; a toad fourteen months, and a beetle three years. 

 This power of outliving scarcity for a time, is of signal use to many animals, whose food 

 cannot be readily obtained ; as is the case with beasts of prey and rapacious birds. But 

 tliis faculty does not belong to such exclusively : wild pigeons have survived twelve 

 days, an antelope twenty days, and a land tortoise eighteen months. Such fasting, 

 however, is detrimental to the system, and can only be considered as one of those sin- 

 gular resources which may be employed in cases where, without it, life would speedily 

 be extinguished. In situations where animals are deprived of their accustomed food, 

 they frequently avoid the effects of starvation, by devouring substances to which their 



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