IIL-MOEBID ANATOMY OF SEROUS MEMBRANES. 



§ 2G5. A right understancliiig of the normal condition and 

 the physiological significance of any organ, has always been 

 deemed the most reliable basis for the determination of what- 

 ever changes it may undergo in disease. This principle holds 

 good most especially in the case of serous membranes. An 

 error which used to be common in the anatomical description of 

 serous membranes, and one w^hicli we occasionally meet with 

 even now, consists in defining them as membranes which differ 

 from the other membranes of the body in possessing a very thin 

 stroma of connective tissue coated w^ith a single layer of j)ave- 

 ment-epithelium. This comparison of serous membranes with 

 other membranous structures and particularly wath mucous mem- 

 branes has led the w^ay to many faulty judgments concerning 

 their morbid anatomy. I regard any such comparison as wholly 

 inadmissible. 



In order to arrive at a just conception of the real nature and 

 significance of the serous membranes, we must refer to a former 

 disquisition (§ 72), in wdiich an attempt was made to show tliat 

 the unformed connective tissue of the body was a continuous 

 ■whole, in wdiich the muscular and nervous fibres, bone and carti- 

 lage, epithelial tissues, &c. , were embedded. A higher degree of 

 structural union between these formal elements and the associated 

 connective tissue, constitutes "organs," such as the muscles, 

 the membranes, the bones, the brain. Between any two adja- 

 cent organs however, there is usually interposed a somewhat 

 thicker layer of connective tissue ; and should those organs be 

 obliged in the discharge of their proper functions to glide upon 

 one another, such movement can only become possible if the 

 intermediate layer of connective tissue splits up into two lamella3, . 

 having their opposed surfaces smooth. Now the visceral and 

 parietal lamella? of any serous sac are just such layers of con- 

 nective tissue ; their membranous character does not denote any 



