138 HOW TO WORK 



examine them carefully, or the observer will not be able to form a 

 correct idea of the structure of the gland- 



238. Liver General Examination. To demonstrate the dif- 

 ferent structures in the liver veiy different processes are required. If 

 the cells alone are to be examined, a freshly-cut surface may be 

 scraped with a sharp knife, and the matter thus removed placed in 

 a drop of water or serum, and covered with the thin glass. The 

 appearance of a cell wall is pretty distinct in water, but this is due 

 partly to the difference in. refractive power of the water and the 

 material of which the so-called cell is composed, and partly to the 

 action of the water itself upon this. If the cells be placed in serum 

 or glycerine, they appear perfectly solid, and no envelope can be 

 discovered, and in some cases sharp points are seen to project from 

 different parts of the cell, a fact which renders the presence of a 

 membrane almost impossible. The liver cell is in fact a mass of 

 soft material the outermost part of which is undergoing change. 



In order to demonstrate the relation which the different elements 

 and structures of the liver bear to- each other, it is advisable to cut 

 a very thin section by means of Valentin's knife,, from the organ 

 when quite fresh ; or thin sections may be taken, from portions of 

 liver which have been hardened in alcohol, chromic acid, &c. The 

 vessels of the liver may sometimes be demonstrated by washing the 

 cells away from a thin section with a stream of water, and then 

 treating it with a little dilute caustic soda. In specimens prepared 

 in this way, however, the capillaries are often quite invisible. From 

 the extreme tenuity of their walls in many cases, not a trace of them 

 can be discovered indeed the existence of the capillary wall can 

 only be proved by filling the vessels with transparent injection in the 

 first instance. 



A consideration of the various elementary tissues of which the 

 different organs of the body are composed, would of itself almost 

 lead to the inference that several different methods must be employed 

 when we desire to demonstrate their individual characters. The 

 medium in which, these different tissues are most satisfactorily exam- 

 ined, depends upon certain physical characters, chemical composi- 

 tion, transparency and refractive power. It is, therefore, next to 

 impossible to demonstrate all the anatomical elements of which an 

 organ is composed in one single specimen. The student should 

 bear in mind that the idea of the organ as it exists during life, is 

 formed from building up, as it were, in his own mind the various 

 structures, the arrangement of which has been demonstrated by 

 several distinct methods of investigation. 



29. On Demonstrating the Structure of the Liver. The inves- 





