234 THE BIICROSCOPE 



fastened with pins. A temperature of 30^ or 40° C. is most suit- 

 able. The thin sections which are made are to be softened in 

 pure water, or water with a little acetic acid. If they are to be 

 stained, they may be placed directly in the carmine, etc. 



Boiling' in vinegar is useful in some cases ; the crystalline 

 lens is obtained by this method. 



A good way to harden tissues is to cut the organ into a 

 number of small pieces, and to suspend them, by means of a 

 thin cord, in a large globe or vessel. Attach the cord to a cork, 

 which must have a number or letter on it corresponding with the 

 same in your pocket-book, with the name, etc. ; the fluid is 

 changed as usual and spirit added. The advantages are that 

 various organs can be put together in one lot of spirit or acid, 

 and a far greater number hardened at once. Care must be taken 

 that too many pieces are not put in the vessel at one time. 



Normal Fluids. 



Fluids which do not alter the appearance of fresh tissues are 

 thus called. Under certain conditions it is advisable to examine 

 the tissues in a fresh condition. These fluids resemble in compo- 

 sition those in which the tissues of the body are bathed. 



1. — Aqueous Humour of the Eye. — This is easily obtained by 

 puncturing the cornea of an eye-ball removed from an ox newly 

 killed. 



2. — Blood Serum. — Pour blood into a tall vessel and allow it to 

 coagulate. After the blood coagulates, run a knife between the 

 upper margin of the clot and the vessel, to permit the clot to con- 

 tract and sink in the serum, which will be squeezed out of the 

 clot. After twenty-four hours draw off the yellow-coloured serum 

 with a pipette. 



3. — Iodised Serum. — Add iodine to blood-serum, prepared as 

 above, until the fluid is of a distinctly yellow colour. This fluid 

 alters the tissues slightly, however, and colours them yellow. A 

 similar solution may be made by adding iodine to amniotic fluid. 



Another method is to add i cc. tincture of iodine and i or 2 

 drops of carbolic acid to 100 cc. fresh amniotic fluid, pericardial 



