xxx INTRODUCTION. 



ON THE PREPARATION OF TISSUES FOR 

 MICROSCOPIC EXAMINATION. 



FRESH TISSUES. 



FRESH tissues as a rule are unsuited for examination with the microscope, though under 

 certain circumstances it is advisable to examine a fresh tissue. When this is done, the tissue 

 must be examined in a fluid which will alter its characters as little as possible ; such fluids 

 are called 



NORMAL OR INDIFFERENT FLUIDS. 



They closely resemble in composition some of the fluids 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 contract 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. 



4. Salt solution (three-quarter per cent). Dissolve 7-5 grammes sodic chloride in 1,000 

 c.c. of distilled water. This is by far the most convenient fluid to employ. Its composition 

 is so near that of lymph the fluid normally bathing the tissues that it alters fresh tissues 

 very slightly. 



HOW TO HARDEN TISSUES. 



GENERAL DIRECTIONS. 



Tissues, however, generally require to be hardened before they can be cut into sections 

 for examination. This is accomplished by exposing the tissue to the action of certain fluids. 



The Material to be employed. The tissues should in all cases be as fresh as possible. 

 When possible the tissues ought to be obtained from the human body, though these in all 

 cases may not be available. It is therefore necessary to use the corresponding organs of some 

 of the lower animals, e.g., cat, dog, rabbit, or pig. Practically their structure is identical with 



