740 LECTURE LTX. 



mediate seat of thought and memory, in the sensorlum ; and for conveying 

 the dictates of the will, and the habitual impulses almost independent of vo- 

 lition, to the muscular parts of the whole frame. 



In what manner these reciprocal impressions are transmitted by the nerves, 

 has never yet been fully determined : but it has long been conjectured, that 

 the medium of communication may bear a considerable analogy to the electrical 

 fluid; and the extreme sensibility of the nerves to the slightest portion of 

 electrical influence, as well as the real and apparently spontaneous excitation of 

 that influence in animal bodies, which have been of late years evinced by gal- 

 vanic experiments, have added very materially to the probability of the opi- 

 nion. An extremely slender fibre, of a substance capable of conducting elec- 

 tricity with perfect freedom, enveloped in a sheath of a perfect nonconductor, 

 would perhaps serve to communicate an impulse, very nearly in the same man- 

 ner, as the nerves appear to do. Indeed nothing can be more fit to constitute 

 a connecting link between material and immaterial beings, than some modi- 

 ficatiori of a fluid, which appears to difter very considerably, in its essential 

 properties, from the common gross matter of the universe, and to possess a 

 subtility and 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 disturbed, 

 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 sys- 

 tematical order. Dr. Cullen has divided them into four classes. Febrile dis- 

 eases, which constitute the first class, consist principally in an increase of 

 the frequency of the pulsations of the heart and arteries, together with an 

 elevation of the temperature, the whole animal economy being at the same 

 time in some measure impaired: they are often accompanied by unnatural or 

 irregular actions of the vessels of particular parts, constituting local inflamma- 

 tions, 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 



