SIMPLE MEMBRANE. 109 



gether ; while in its higher developments, as in bone, &c., it mani- 

 fests the vital functions characteristic of the tissue of which it forms 

 a part. The latter are, however, always of a low grade, as mere 

 nutrition and reparation, since all the tissues in which it abounds 

 are useful rather from their mechanical than their vital properties. 

 Distribution. It abounds in bone and cartilage, and in the morbid 

 developments already mentioned. 



In pathological states, homogeneous substance may undergo a fatty 

 degeneration ( Wedl), oil-globules being deposited in it. Pigmentary 

 substances are also often found in it. 



CHAPTEE II. 



SIMPLE MEMBKANE. 



SIMPLE membrane usually appears as a very thin, transparent, 

 and perfectly structureless layer of coagulated albumen or plasma, 

 often not more than 3I5 J 01J of an inch in thickness. It is nourished 

 by vessels lying near or under it, but is never penetrated by any 

 vessel, nerve, or, indeed, by any other tissue whatever. It is entirely 

 imperforate at every part, the highest powers of the microscope 

 never revealing any pores, or openings of any kind. Forming, 

 therefore, a complete barrier between the structures on its opposite 

 sides, it has, in some parts, been termed a limitary membrane. 



The posterior layer of the capsule of the crystalline lens affords 

 an excellent illustration of this kind of tissue. ,-,. . 



rig. 47. 



Being structureless and transparent, it can, how- 

 ever, only be seen when accidental folds or other 

 irregularities are formed. (Queckett, p. 116.) 



In some case, however, granules also appear in 

 simple membrane ; and in a third form of it dis- 

 tinct spots appear, which have been regarded as 

 nuclei ; and it may be broken up into separate 

 portions, each containing one of these. (Fig. 47.) 



If the Simplest form is Solidified albumen Or . Basement membrane of 

 intra-glandular lympha- 



plasma, the second is probably the same sub- tics. 



