40 PRIMARY TISSUES I SEROUS MEMBRANES. 



and has sometimes been purposely effected, does not produce 

 any disorder in the general functions of the body. In blow- 

 ing the nose violently, some part of the membrane lining its 

 cavity has occasionally given way, so as to allow air to pass 

 into the areolar tissue of the face, and especially into that 

 contained in the eyelids, which is particularly loose ; an enor- 

 mous swelling of these parts then takes place, presenting a 

 very frightful appearance, but not attended with the least 

 danger, and subsiding of itself in a few days. This swelling 

 presents a character to the touch quite different from that 

 which would be occasioned by a similar distension with liquid; 

 for it gives somewhat of the crackling feel that is occasioned 

 by pressing on a blown bladder. A similar inflation of the 

 areolar tissue of the body has sometimes occurred from the 

 formation of an aperture, by disease or injury, in the walls of 

 the lungs or air-passages, and the consequent escape of air 

 during the act of breathing : in one remarkable case of this 

 kind, the skin of the whole body was so tightly distended 

 with air as to resemble a drum. It is intentionally practised 

 by butchers, who " blow up " the areolar tissue of their veal, 

 in order to increase its plumpness of aspect; and the in- 

 flation of the areolar tissue of the head, in the living state, 

 has been sometimes practised by impostors, in order to excite 

 commiseration. 



28. Fibres and shreds of nbro-membrane, resembling those 

 of which areolar tissue is composed, may be so interwoven as 

 to form a continuous sheet of membrane, having a smooth 

 and glistening surface j and in this manner are produced the 

 Serous Membranes that line the different cavities in which the 

 viscera (or organs contained within the skull, the chest, and 

 the abdomen) are lodged. The peculiar manner in which 

 these membranes are arranged, will be explained hereafter 

 ( 43). One of their surfaces is always free or unattached, 

 whilst the other is in contact with the outer wall of the 

 cavity ; and from the free surface, which is covered with a 

 layer of flattened epithelium-cells (fig. 10), a serous fluid is 

 exhaled, which adds to its smoothness. It is by an accumula- 

 tion of this fluid, that dropsies of the cavities are produced, 

 such as water on the brain, or in the chest. 



29. By the union of fibres of a stronger kind, those firmer 

 tissues are produced, which are employed wherever a greater 



