APPENDIX 321 



VII. TREATMENT OF LIVING TISSUES WITH 

 METHYLENE BLUE. 



A dilute solution of methylene blue applied to a living tissue, 

 exposed to the air, stains for a time nerve-endings and nerve - 

 fibrils without staining other structures (except some connective- 

 tissue cells, leucocytes and nuclei). The maximum stain is in 

 about half-an-hour, but it varies in different tissues and in 

 different circumstances. Then the nerve-endings begin to de- 

 colourize, and the medullated nerve fibres and other structures 

 begin to stain. 



For the tissues of cold-blooded animals, if sufficiently thin to 

 be observed without cutting sections, the method given in the 

 text, p. 125, is perhaps the best. The same method may be 

 employed for sections of tissues which are sufficiently firm to be 

 cut free-hand in the fresh state. 



When the tissue is not exposed to air, the nerve-endings still 

 take up methylene blue, but decolourize it ; the colour returning 

 on exposure to air. Thus the fluid may be injected into the 

 body, and this is generally the best method in the warm-blooded 

 animal. The injection may be made in either of the following 

 ways in an anaesthetized animal : 



(a) A. I p.c. solution of methylene blue in normal salt 

 solution is injected into a blood vessel until the skin in an 

 exposed part, such as the ear, is light blue. The animal is then 

 left for half-an-hour to an hour, bled, the tissue to be investigated 

 cut out, moistened with a normal fluid, and exposed to air. 



(6) Injections of methylene blue are made at intervals of 15 

 minutes until the animal dies. 



(c) The animal is bled to death, 1 p.c. methylene blue 

 injected into an artery supplying the part to be investigated. 



The specimen when covered with a cover-slip rapidly loses its 

 tint, so that for examination with a high power it is generally 



L. 21 



