SECTION OF FROZEN MUSCLE. 123 



tissue in order to obtain transverse sections of the 

 fibres in wbat has been thought a completely un- 

 altered state. It may be doubted, though, whether 

 the muscular substance does not undergo some 

 structural alteration either in the freezing or in the 

 subsequent thawing. Yet, as it is frequently em- 

 ployed for this tissue, and is of considerable value 

 in special investigations into the structure of other 

 tissues and organs, the method may be here de- 

 scribed. 



Preparation 14. Section of frozen muscle. 

 The best and simplest mode of freezing a tissue 

 is that recommended by Urban Pritchard. A solid 

 cylinder of copper (1 inch wide and 3 inches long), 

 with flat ends, is placed for a few minutes in a 

 freezing mixture composed of equal parts of pounded 

 ice and salt, by which it is cooled to considerably 

 below the freezing-point. The copper cylinder is 

 then removed, wiped quite dry with a cloth, and a 

 piece of flannel is wrapped three or four times round 

 it, leaving one of the flat ends exposed. The muscle, 

 which may conveniently be taken from the leg of a 

 frog, is cut across near its middle and one of the 

 halves is placed with its cut surface on the flat end 

 of the copper block in a drop of gum arabic solution. 

 This as well as the tissue very speedily becomes 

 frozen throughout, adheres to the copper, and then, 

 the block being held in the left hand, sections are 

 made of the muscle with a dry razor, which should 

 have been previously cooled by contact with the 

 vessel containing the freezing mixture, and the 

 sections are at once transferred to a slide and 

 covered, either in serum, or, better, without the 

 addition of any fluid. 



Sections made by freezing possess the advantage 

 that, since they have not been submitted to any 

 coagulating reagent, they may be treated with 

 nitrate of silver, chloride of gold, and other fluids 

 which are of value only when the tissues are per- 

 fectly fresh. 



