292 APPENDIX 



b. by cutting a section with a Valentine's knife, 

 i.e., a double -bladed knife, in which the distance of the 

 blades from one another can be varied; 



c. by cutting off a thin piece with fine-pointed 

 scissors ; 



d. by tearing off a small strip with fine-pointed 

 forceps if the tissue is fibrous. 



After examining the piece of tissue, normal salt 

 solution should be allowed to run under the cover-slip, 

 the cover-slip pressed, an examination made, the cover- 

 slip tapped smartly two or three times to break up the 

 tissue, and examined again. Other pieces should be 

 'similarly treated with fresh aqueous humour, fresh 

 serum, 1 p.c., 2 p.c., 5 p.c. sodium chloride, and with 

 dilute acids and alkalis. 



Membranous structures may be pinned out over 

 a hole in a stage. 



Motile cells should be examined in a hanging drop 

 as well as on the slide. 



Freezing a tissue alters more or less markedly the 

 living appearance ; the alteration appears to be chiefly 

 due to the formation of ice crystals. To avoid this the 

 piece of tissue may be soaked for a quarter of an hour 

 in fresh white of egg or in a dilute solution of gum in 

 salt solution, but this of itself causes considerable 

 changes. For the method of cutting frozen sections 

 cp. Lesson vir. 



B. Dissociating fluids. These are fluids which, whilst 

 preserving certain parts of a tissue, dissolve or partially dissolve 

 others, principally the cementing or ground substances, so that 

 the former can be isolated by teasing or shaking. As a rule the 





