OF SIMPLE MEMBRANE; ITS FORMATION AND PROPERTIES. 139 



(Fig. 51) and a distinct fibrous tissue (Fig. 52). Here, too, it is possible that, 

 although the fibres do not themselves originate in the transformation of cells, 

 the cells of the cartilage may exert such a determining agency in their produc- 

 tion, as appears to proceed from the nuclei in the cases previously referred to. 

 Of all the varieties of Fibrous tissue thus generated, it may be stated that their 

 function is simply mechanical ; that consequently the performance of that func- 

 tion does not depend upon a continuance of vital activity; and that they do not 

 seem to possess that power of self-formation which is characteristic of the cellular 

 tissues, but for the most part depend, for their production, the maintenance, and 

 regeneration after injury, upon the formative power of the Blood ( 224). 



119. Of Simple Membrane; its Formation and Properties. In many parts 

 of the Animal body, we meet with membranous expansions of extreme delicacy 

 and transparency, in which no definite structure can be discovered ; and these 

 seem, like the simple fibres just described, to have been formed rather directly 

 from the nutritive fluid, than indirectly by any process of transformation. The 

 characters of this kind of membrane were first pointed out by Mr. Bowman 1 

 and Prof. Goodsir; 2 by the former of whom it was named &ase?we7^-membrane, 

 as being the foundation or resting-place for the epithelial or epidermic cells 

 which usually lie upon its free surface ; whilst by the latter it was termed the 

 primary or germinal membrane, as furnishing (in his opinion) the germs of 

 those cells. In its very simplest form, the basement-membrane is a pellicle of 

 such extreme delicacy, that its thickness scarcely admits of being measured ; it 

 is to all appearance perfectly homogeneous, and presents not the slightest trace 

 of structure under the highest powers of the microscope, appearing like a thin 

 film of coagulated gelatine. Examples of this kind may easily be procured, by 

 acting on the inner layer of any bivalve shell with dilute acid ; this dissolves 

 away the calcareous matter, and leaves the basement-membrane. In other cases, 

 however, the membrane is not so homogeneous ; a number of minute granules 

 being scattered, with more or less of uniformity, through the transparent sub- 

 stance. And we not unfrequently find, in the place of these uniformly dis- 

 tributed granules, a series of distinct spots, arranged at equal or variable dis- 

 tances, and lying in different directions ; of this Prof. Goodsir has adduced a 

 good example in the membrane of the intra-glandular lymphatics. 3 Moreover, 

 the membrane thus constituted is disposed to break up into portions of equal 

 size, each of which contains one of these spots ; whilst in the more homogeneous 

 forms previously described, no appearance of any definite arrangement is per- 

 ceptible when they are torn. Hence it would seem as if the first and simplest 

 form were produced by the simple consolidation of a thin layer of homogeneous 

 fluid ] the second by a layer of such fluid, including nuclear particles ; and the 

 third by the coalescence of flattened cells, whose further development has been 

 checked, but whose nuclei may still continue % to perform their characteristic 

 functions. It is probable that the primary membrane exists, under one or 

 other of these forms, on all the free surfaces of the body ; though it cannot 

 be everywhere demonstrated. Thus it appears to constitute ^the outer layer of 

 the true Skin, lying between its fibrous substance and the epidermis ; it lines 

 all the cavities formed by Mucous membranes, and is prolonged into all the 

 ducts and ultimate follicles and tubuli of Glands which are connected with them, 

 being, indeed, with the exception of the epithelial cells which cover its inner sur- 

 face, the sole constituent of some of these ; it forms the innermost layer, also, 

 of the Serous and Synovial membranes, there, also, supporting the epithelium ; 



1 See his memoir "On the Structure and Uses of the Malpighian Bodies of the Kidney" 

 in the "Philos. Transact.," 1842; and the "Cyclopedia of Anatomy and Physiology," 

 vol. iii., Art. "Mucous Membrane." 



2 "Anatomical and Pathological Observations," p. 3. 



3 "Anatomical and Physiological Observations," pp. 46, 47. 



