2. AS EVACUANTS—_by occasioning an effusion of Fluids_. In this case the vesicated part may be considered in the light of a new excretory organ, the formation of which requires the establishment of a new current or determination of blood; so long as the discharge continues, so long will there be an especial demand of blood in the blistered part, and a consequent derivation of the circulation from the inflamed and engorged vessels of the neighbouring organs.[174] The nature of the fluid effused is at first serous, but after some time it becomes purulent, and this stage of its operation must be considered as, by far, the most beneficial; hence the great advantages derived from a “_perpetual blister_.” 3. AS GENERAL STIMULANTS, _by raising the vigour of the circulation_.[175] That Blisters have such a tendency there exist too many proofs to allow us to doubt. Hence in fevers they frequently prove valuable auxiliaries, but since the application of any stimulus, in such diseases, must be regulated by the degree of excitement, it is evident that they can only be made with success in particular stages; this simple fact will at once explain the cause of that want of unanimity in Physicians with respect to the value of blisters in febrile diseases. Rush considered that there was one particular period, in the course of a continued fever, intermediate between its stage of high excitement and the appearance of a collapse, in which blisters will generally produce unequivocal good effects, and to this he gave the name of the _Blistering point_. 4. AS ANTISPASMODICS.—_Relieving pain through the medium of Contiguous Sympathy._ This effect would frequently appear to be independent of the operations above enumerated; a similar principle seems to exist with regard to the _pain_ excited by blisters, which may also be applied to the explanation of the advantages derived from them in several diseases. It has long been remarked that, by exciting one pain we may often relieve another, and hence blisters afford relief in tooth-ache, and other painful affections. Epilepsy and Hysteria, arising from irritation, have been removed by such applications, apparently from their exciting powers.