SECEETIONS. 81 



recently dead, an injection be thrown, composed of gelatine, 

 mingled with vermilion finely powdered, the fluid part of the 

 injection will escape into the adjoining tissues, leaving the 

 vermilion particles in the vessels ; thus imitating what seems 

 to take place during life. 



148. In fact, inhalation, already explained, and exha- 

 lation are strictly analogous, and take place in the same 

 way ; and their activity depends on the spongy and vascular 

 character of the tissue. In another sense, these functions are 

 in the inverse ratio of each other. By pressure on the veins, 

 the exhalation into depending parts may be much increased. 



149. Seat of the Exhalation. Exhalations are either 

 external, that is, on the surface of the body ; or internal, 

 that is, on the surface of the internal cavities. 



150. External exhalation must not be confounded 

 with perspiration, or production of sweat ; it takes place on 

 the surface of the lungs as well as on that of the body, and is 

 called insensible transpiration, because, being evaporated by 

 the air, it escapes our notice. Men and animals lose much 

 daily by insensible transpiration, which, of course, is as con- 

 stantly restored; according to Sanctorius, the loss by insensible 

 transpiration in man amounts to fths of the whole daily loss. 

 The evaporation from the surface of the body varies with 

 many circumstances, as climate, &c. ; the escape of carbonic 

 acid gMs from the lungs is by means of exhalation merely. 



151. The serous membranes found in the interior of the 

 large cavities of the body are the seat of internal exhalations, 

 consisting chiefly of water, and a few salts, mixed with a 

 small quantity of animal matter. The exhalation which 

 takes place on these surfaces has an exact counterpoise in the 

 absorption going on at the same time ; when this is disturbed 

 the fluid accumulates, and dropsies take place, which receive 

 names according to their localities : hydrocephalus, in the 

 head ;. ascites, in the abdomen ; hydrothorax, in the chest 

 and pleurae ; and hydrops pericardii when the accumulation 

 takes place within the cavity of the pericardium. 



SECRETIONS. 



152. The secretions are special humours, formed at the 

 expense of the blood, in and by organs destined especially to 

 eliminate them from the blood. 



153. They may take place on the surface of membranes, 



