CHAPTER Y. 



GENERAL HISTOLOGY. 



STUDIED under the microscope, the organs are found to be 

 composed of tissues (muscular tissue, nervous tissue, glandular 

 tissue, etc.), and the tissues to be built up of cells, together 

 with certain cell products. 



To make out the form and structure of the cells, a small piece 

 of the tissue may be teased to pieces in a dilute solution (-75 per 

 cent.) of common salt (normal saline) with two needles on a glass 

 slide. The teased tissue must then be covered with a cover-glass 

 and examined. But to make out the relations to each other of the 

 cells in a tissue, thin sections of the tissue must be cut. To bring 

 out clearly the structure of a cell or of a tissue, advantage is 

 taken of the fact that different parts of a cell, and different cells 

 in a tissue, are differently affected by certain re-agents, such as 

 dilute acid or staining fluids. The cells or tissues so prepared 

 must be mounted either temporarily for immediate study in 

 normal saline solution or glycerine, or permanently in glycerine 

 or Canada balsam. 1 



1 For the guidance of the student the following hints on section-cutting may 

 be useful : 



1. Cut a small fragment fresh from the organ to be examined. 



2. Place in (a) osmic acid, 1 per cent., for two or three minutes; or (b) in 

 chromic acid, 5 per cent., for twenty-four hours ; or (c) in Kleinemberg's picric 

 acid for eighteen hours. The object will thus be hardened. 



3. Place in 50 per cent, alcohol for twenty-four hours, then 70 per cent, alcohol 

 for twelve hours, 80 per cent, alcohol for six hours, and transfer to 90 per cent, 

 alcohol. This removes the water. 



4. Place in staining fluid until sufficiently deeply stained. (1) Hsematoxalin, 

 (2) picro -carmine, (3) eosin, and (4) borax-carmine, are the most useful re-agents. 



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