HISTOLOGICAL METHODS. 159 



289 A. Method of Digestion. Artificial digestion in 

 a fluid containing pepsine and hydrochloric acid has been 

 used for causing striped muscle to cleave into discs. It may 

 also be employed for softening and clarifying white fibrous 

 tissue. The manner in which it may be applied to the skin 

 in studying the arrangements of its elastic fibres is detailed 

 in 223 b. 



MECHANICAL DISSOCIATION OF TISSUE ELEMENTS. 



290. Tissue elements may be separated by various 

 mechanical methods. 



a. By dissection with needles. Those most suitable are 

 thick sewing needles fixed in strong handles (Figs. 54 and 34). 



FIG. 54. Dissecting needle. 



Delicate textures and organs should be dissected under 

 fluid. 



b. By shaking. This is a most useful method of 

 dissociation, e.g., the lymph corpuscles may be readily 

 freed from the adenoid tissue in a section of lymphatic 

 gland in this way ( 1 1 o). The shaking is performed in a 

 test tube containing some desirable fluid. 



c. By pressure under the cover-glass, one is often able 

 to separate tissue elements so as to display them effectively. 

 The mode of demonstrating nerve cells in the fresh brain, 

 detailed in 247, c, is a good example of this method, and 

 there are many others with which every one who works with 

 the microscope for some time, soon becomes familiar. 



It will be readily understood that the various fluids for 

 softening connective substances facilitate the mechanical dis- 

 sociation of tissue elements. 



METHODS OF MAKING SECTIONS. 



291. Saw. Sections of unsoftened bone are made with 

 a fine saw. The scratches thereby produced, are got rid of, 

 and the sections at the same time ground sufficiently thin 

 upon a stone, after the manner already described ( 1 1 8). 



