16 DISEASES CLASS I. 1. 2. 3. 



vessels, which are generally cooler than the internal parts of the 

 system, excites them into greater action; and pleasurable sensa- 

 tion is the consequence of these increased actions of the vessels 

 of the skin. From considering all these circumstances, it ap- 

 pears that it is not the evacuation by sweats, but the continued 

 stimulus, which causes and supports those sweats which is ser- 

 viceable in preventing the returns of fever-fits. And that sweats 

 too long continued, or induced by too great stimulus of warmth, 

 clothes, or medicines, greatly injure the patient by increasing in- 

 flammation, or by exhausting the sensorial power. See Class I. 

 1.2. 14. 



Secondly, The sweats produced by exercise or labour are of 

 the warm kind; as they originate from the increased action of 

 the capillaries of the skin, owing to their being more powerfully 

 stimulated by the greater velocity of the blood, and by a greater 

 quantity of it passing through them in a given time. For the 

 blood during violent exercise is carried forwards by the action 

 of the muscles faster in the arteries, than it can be taken up by 

 the veins; as appears by the redness of the skin. And from 

 the consequent sweats, it is evinced, that the secretory vessels 

 of the skin during exercise pour out the perspirable matter faster, 

 than the mouths of the absorbent vessels can drink it up. Which 

 mouths are not exposed to the increased muscular action, or to 

 the stimulus of the increased velocity and quantity of the blood, 

 but to the cool air, 



Thirdly, The increased secretion of perspirable matter occasion- 

 ed by the stimulus of external heat belongs likewise to this place; 

 as it is caused by the increased motions of the capillary vessels; 

 which thus separate from the blood more perspirable matter, 

 than the mouths of their correspondent absorbent vessels can take 

 up; though these also are stimulated by external heat into more 

 energetic action. If the. air be stationary, as in a small room, 

 or bed with closed curtains, the sweat stands in drops on the skin 

 for want of a quicker exhalation proportioned to the quicker se- 

 cretion. 



A fourth variety of warm perspiration is that occasioned by 

 stimulating drugs, of which opium and alcohol are the most 

 powerful; and next to these the spices, volatile alkali, and neu- 

 tral salts, especially sea-salt; that much of the aqueous part of 

 the blood is dissipated by the use of these drugs, is evinced by 

 the great thirst, which occurs a few hours after the use of them. 

 See Art. III. 2. I. 



We may from hence understand, that the increase of this 

 secretion of perspirable matter by artificial means, must be fol- 

 lowed by debility and emaciation. When this is done by taking 



