192 DETAILED SYNTHESIS. 



are albuminous, filled with fat, and kept in their position 

 by sinewy fibres. There may be one or many cells to- 

 gether, and they can increase or diminish as any other 

 cells do. 



Remark. In milk, the fat or butter is contained in albuminoid cells, 

 that must be broken by churning, in order that the butter may be gath- 

 ered ; and the more perfectly this is done, and the more completely the 

 inclosing cell is removed from the butter, and is left pure, the better 

 it will keep. If rancid, it can be greatly unproved, if not made sweet, 

 by thoroughly washing out the decomposing cells. This can be done 

 best in sweet milk. (See Fig. 124.) 



199. There are also THREE COMPOUND MEMBRANES 

 of very considerable importance, to be described before 

 proceeding to the consideration of organs; they are 

 called the skin, and mucous and serous membranes, and 

 correspond to the three general surfaces of the body ; the 

 external, the air and food, and the internal surfaces, fur- 

 nished with the three kinds of cells, the epidermic or 

 cuticular, the epithelial or mucous, and the tesselated or 

 serous, and lubricated by the three surface-fluids, oil, 

 mucus, and serum. 



200. THE SKIN, as already stated, is COMPOSED of a 

 thick under part formed of sinewy fibres, woven so as 

 to form meshes that are occupied by the Blood-tubes, 

 red and white, by the nerves, and by perspiratory, hair, 

 and sebaceous glands, and their outlets. The uneven or 

 papillated surface of this layer is covered by the exqui- 

 sitely delicate basement membrane from which spring 

 up the cells that, filled with watery fluid and a little 

 horny matter, become dry, flattened scales as they reach 

 the surface. 



201. THE MUCOUS MEMBRANE is correspondingly 

 CONSTITUTED of three layers, the sinewy having Blood- 

 tubes, nerves, and glands in its meshes, a basement mem- 

 brane upon it, and one or several layers of cells forming 

 the free surface. 



What said of milk and butter? 199. What said of ? 200. How ? 201. How 

 T What Fig. illustrates compound membrane ? 



