IN TROD UCTION. 



XXXV 



for other soluble ferments. I c.c. of the glycerine filtrate is added to 19 c.c. of I per cent, 

 solution of sodic carbonate. The fluid becomes turbid, but after filtration a pale yellow fluid 

 is obtained. The tissue to be digested is placed in this fluid, and the whole is kept at a tem- 

 perature of 40 C. in a water bath as directed at p. 92. Sections of softened bone digested by 

 this method are preserved in a 10 per cent, solution of common salt (Birch). 



METHODS OF TEASING A TISSUE. 



Take only a small piece of tissue, and place it on a slide in a small drop of the fluid in 

 which it is to be mounted, e.g. glycerine. Fix one end of the tissue with a strong needle in a 

 handle, and tear in the direction of the fibres with the other needle. The low power must be 

 used from time to time, to ascertain when the component parts are sufficiently isolated. It is 

 very desirable to have a proper background, so that the object to be teased may be distinctly 

 seen ; for a coloured object a small piece of white bibulous paper answers admirably, and a trans- 

 parent object is generally best seen on a dark surface. A good plan is to have a narrow white 

 line painted along the edge of the work-table. The same result is obtained by having a small 

 slab, one-half of which is glazed white and the other black. 



RANVIER'S PHOTOPHORE. 



The following little arrangement devised by Ranvier is of great value for this pur- 

 pose. It is called a photophore (fig. 15). It consists of a small mahogany box about four 

 inches square ; one side is open and so is the top. The lid is formed of a glass plate. Into 

 the box a mirror is fixed at an angle of 3O-35. This arrange- 

 ment reflects the light through the preparation. If it be desired 

 to work with a black background, all that is required is to place 

 a black card over the mirror. This simple arrangement is of 



the utmost value, and when in use has simply to be directed with 



... . , T . ,, . i t, Fig. IS- RANVIER'S PHOTOPHORE. 



its mirror towards a window. It is well to have a bent piece One-sixth Natural Size 



of wire, with a ring formed on it and attached to the back of the 



box, for receiving a small magnifying lens. Each student should be provided with such an 

 arrangement. He can easily make one for himself by taking an ordinary small cigar-box 

 without a lid, and placing in it a mirror at an angle of 30^-3 5. On the upper side make 

 a square hole, and into this fit a glass plate. 



SIMPLE OR DISSECTING MICROSCOPE. 



In teasing or dissociating a tissue it is often of great value to 

 use an ordinary dissecting microscope. The form devised by Briicke 

 and made by Hartnack is useful, but it is expensive. For practical 

 purposes I find that the form, fig. 16, made by Swift, is a most useful 

 and handy instrument. 



Fig. 16. SWIFT'S SIMPLE 



DISSECTING MICROSCOPE. 



One-sixth Natural Size. 



d2 



