PART II. 



MICROSCOPICAL TECHNIQUE. 



I. THE PREPARATION OF MICROSCOPICAL 



SPECIMENS. 



REVISED BY LAWSON G. LOWREY. 



The methods of fundamental importance, which are likely to be em- 

 ployed by students who are beginning their histological studies, are here 

 given. Further information may be obtained from "The Microtomist's 

 Vade Mecum" by A. B. Lee (Blakiston, Philadelphia) and from Mallory 

 and Wright's "Pathological Technique" (Saunders, Philadelphia). The 

 former deals with the subject from the point of view of general biology; 

 the latter is particularly adapted to the needs of medical students. 



FRESH TISSUES. 



Certain tissues may be studied advantageously in a fresh condition. 

 They are simply spread on a clean glass slide, covered and examined. 

 Desquamated epithelial cells, spermatozoa, blood, and other fluids con- 

 taining cells, may be treated in this way. But structures such as muscles, 

 tendons, nerves, connective tissue, etc., must first be "teased" that is, 

 torn into very small fragments or spread into a thin layer with a pair of 

 fine needles. 



The "parenchymatous" organs, or other structures which cannot be 

 investigated satisfactorily by the above methods, must be sectioned or 

 macerated. The old methods of making free-hand sections of the object 

 held between pieces of pith, or of making sections with a double bladed 

 knife, have been superseded in most laboratories by the freezing method. 

 This method is often serviceable in histology, and is indispensable in 

 the rapid diagnosis of pathological conditions. 



Blocks of tissue not over 5 mm. thick are moistened with water, placed 

 on the carrier of a special form of microtome and frozen by a jet of carbon 

 dioxide proceeding from a tank of the compressed gas. Sections 10 to 15/4 

 thick may be chiselled from the block of tissue and unrolled by transferring 

 to a dish of 0.6 per cent, sodium chloride solution. They are floated on a 

 slide, covered and examined. 



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