ON ANIMAL LIFE. 579 



an activity, which entitle it to a superior rank in the order of created 

 substances. 



When all the functions of animal life are carried on in their perfect and 

 natural manner, the animal is said to be in health : when they are dis- 

 turbed, a state of disease ensues. The diseases to which the human frame 

 is liable are so various and irregular, that they cannot easily be reduced 

 to any systematical order. Dr. Cullen has divided them into four classes. 

 Febrile diseases, which constitute the first class, consist principally in an 

 increase of the frequency of the pulsations of the heart and arteries, toge- 

 ther with an elevation of the temperature, the whole animal economy 

 being at the same time in some measure impaired : they are often accom- 

 panied by unnatural or irregular actions of the vessels of particular parts, 

 constituting local inflammations, which were formerly considered as a 

 derivation of diseased humours, falling on those parts : thus, a pleurisy 

 is a fever, with an inflammation of the membrane lining the chest. The 

 incapacity of a part to perform its functions, upon the application of a 

 natural stimulus, or perhaps more frequently the incapacity of the nerves 

 to transmit to it the dictates of the mind, constitutes a palsy : such 

 derangements, and others, by which the actions of the nervous system are 

 peculiarly impaired, form the class of neuroses, including spasmodic affec- 

 tions, madness, melancholy, and epilepsy. A general derangement of the 

 system, without fever, or any peculiar debility of the nerves, constitutes 

 the class of cachectic diseases, such as atrophy, consumption, scrofula, 

 and dropsy. Besides these diseases, we have a fourth class, consisting of 

 local affections only, such as blindness, deafness, tumours, and luxations. 



Notwithstanding the labours of men of the greatest learning and genius, 

 continued for many centuries, it must be confessed that the art of healing 

 diseases is still in a state of great imperfection. Happily, however, for 

 mankind, we may observe in almost all cases, where the offending cause is 

 discoverable, and where the system is not at once overwhelmed by its mag- 

 nitude, a wise and wonderful provision for removing it, by a mechanism 

 admirably simple and efficacious ; and it is reasonable to conclude, where 

 the cause is more obscure, that the same benevolent Providence has em- 

 ployed agents equally well adapted for counteracting it, although their 

 operations are utterly beyond the reach of human penetration. 



On the subjects embraced in this Lecture, the reader may consult Roget's Bridg- 

 water Treatise ; Darwin's Zoonomia, 4 vols. 1804 ; or the great works of Buffon, 

 Histoire Naturelle, 127 vols. Paris, 1799-1808, and Cuvier, Le Regne Animal, 

 translated, in 16 vols. Lond. 1824-33. Liebig's Animal Chemistry, 8vo. 1843. 



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