CENTRES OF NUTRITION. 3 



membrane.* In a germinal membrane, the nutritive or germinal 

 centres are arranged at equal or variable distances, and in certain 

 directions, in the substance of a fine transparent membrane. A 

 germinal membrane is occasionally found to break up into por- 

 tions of equal size, each of which contains one of the germinal 

 centres. From this it is perceived, that a germinal membrane 

 consists of cells, with their cavities flattened, so that their walls 

 form the membrane, by cohering at their edges, and their nuclei 

 remain in its substance as the germinal centres. 



Germinal membranes are only met with on the free surfaces of 

 parts or organs. One surface of the membrane is therefore 

 attached, and is applied upon a layer of areolar texture, inter- 

 mixed with a more or less rich network of capillary vessels. 

 The other surface is free, and it is on it only that the developed 

 or secondary cells of its germinal spots are attached. These 

 secondary cells are at first contained between the two layers of 

 the membrane, these layers being the opposite walls of each of its 

 component cells. When fully developed, the secondary cells 

 carry forward the anterior layer, which is always the thinnest, 

 leaving the nuclei or germinal centres in the substance of the 

 posterior layer, in close contact with the blood-vessels. 



Of the forces which exist in connection with centres of nutri- 

 tion, nothing very definite can yet be stated. When this branch 

 of inquiry shall have been opened up, we shall expect to have a 

 science of organic forces, bearing direct relations to anatomy, the 

 science of organic forms. J. G. 



* The membranous tubes of glands on which the epithelium is situated, was described by 

 Henle, MiiUer's "Archiv," 1839. Mr. Bowman (Phil. Trans. 1842) " On the Structure and 

 Use of the Malpighian Bodies of the Kidney," &c., has applied to the membrane of these 

 tubes the very appropriate name of Basement Membrane. This membrane I consider to be 

 a primary or germinal membrane. The term, basement membrane, is good as involving no 

 hypothesis ; it is therefore a most appropriate descriptive term. I have always considered 

 the basement membrane, or elementary membrane of glands, as a form of the primary cells 

 of glands, and the source of the secondary or secreting cells, and have therefore been in the 

 habit of naming it primary, or germinal membrane. Mr. Bowman considers it to be simple, 

 or homogeneous. This is true as far as it contains no blood-vessels, and as regards its ex- 

 ternal or attached layer ; but as in its original condition it consists of cells, and when perfect 

 contains nuclei at equal or variable distances, I do not consider it as simply molecular. 

 These nuclei, or germinal spots, may be certain of the epithelial cells, which become mother 

 cells, between the two layers of the membrane ; or cells belonging to the order of the 

 nuclear fibres of Valentin and Henlo. 



