*> 



198 



I shall on another occasion, explain the mechanism of sucking, oi' 

 panting, and of the efforts by which the muscles of the thorax fix the pa- 

 rietes of that cavity, so that it may serve as -a fixed point of the other 

 muscles of the trunk and the limbs. 



Respiration is besides employed in the formation of the voice, but the 

 voice and the different modifications of which it is capable, will form the 

 subject of a separate chapter*. 



LXXXVII. Of cutaneous perspirations. An abundant vapour is continu- 

 ally exhaling from the whole surface of the body, and is called the insen- 

 sible perspiration, when in a state of gas in the air which holds it in solu- 

 tion, it then eludes our sight; it isValled sweat, when in greater quantity 

 and in a liquid form. Sweat differs, therefore, from insensible perspira- 

 tion, only by the condition in which it appears, and it is sufficient for its 

 production, that the air should be incapable of reducing it into vapour, 

 whether from an increased secretion by the skin, or from the dampness 

 and consequent diminished solvent powers of the atmosphere. The insen- 

 sible perspiration is constantly escaping through the innumerable pores in 

 the parietes of the minute arteries of the integuments; it oozes in the in- 

 terstices of the scales of the skin; the air which immediately surrounds 

 our body, becomes saturated with it, and carries it off, as soon as it is re- 

 newed. There is the greatest resemblance, between the cutaneous pers- 

 piration and the pulmonary exhalation; both are mere arterial exhalations, 

 and the mucous membrane, which lines the canals along which the air is 

 transmitted, is a mere prolongation of the skin into these organs and into 

 the digestive tube. The surface from which the cutaneous perspiration 

 it exhaled, is not quite so considerable as that from which the pulmonary 

 exhalation arises, since it is reckoned at only fifteen square feet, in a man 

 of middle size. These two secretions are supplementary to each other ; 



* The a&thor has neglected to notice the state of respiration during the most active 

 voluntary motions. Muscular exertion? especially when considerable, is preceded by 

 a long and deep inspiration, the glottis is closed*, the diaphragm and respiratory mus- 

 cles of the chest are contracted, and the reaction of the abdominal muscles cause the 

 contents of the abdomen to be pressed upon in all directions. At the same time that 

 the respiratory muscles are exerted, those of the face are associated, in the increased 

 action, in consequence of the latter receiving some nerves from the same class, (see 

 the notes in the APPENDIX on the different orders and functions of the voluntary 

 system of nerves) and the jaws are forcibly pressed together. By this action of the 

 muscles engaged in respiration, the chest is rendered capacious, and the strength is 

 greatly increased, because the trunk of the body is thus rendered immoveable in re- 

 spect to its individual parts, the muscles arise from fixed points, and consequently, wield 

 the members of the body, with their full energy. HALLER appears to be correct in 

 concluding that, under a" state of increased action of the muscles, the flow of blood b 

 comes greater towards the head, and thus the nervous energy is increased, and amply 

 generated, by means of this augmented flo'y, so as to keep up the muscular action for 

 a longer period than otherwise would be the case. During violent exertions, also, the 

 return of blood from the brain is in some degree impeded. 



The physiological s.tate of muscular actions, as they are related to the mechanical 

 function of respiration, is very happily described by Shakspeare, where he makes the 

 fifth Henry encourage his soldiers at the siege of Harfieur : 

 Stiffen the sinews,' summon up the blood, 



Now set the teeth, and stretch the nostrils wide ; 



Hold hard the breath, and bend up every spirit, 



To his full height. 



In vomiting also, and in the action of expelling the faeces and the contents of the blad- 

 der, the thoracic and abdominal muscles of respiration are brought into action. Cop- 

 land. 



