336 WALTER E. DANDY 



attachment posteriorly, so that the entering nerves may be 

 studied in their true relations, without tearing or distortion. 



We have used almost exclusively" the specific methylene blue 

 intra vitam method of staining the nerves. For the details of 

 this technique we are greatly indebted to the excellent contri- 

 bution by J. Gordon Wilson (12). Three essentials are necessary 

 for the successful use of this stain: the exsanguination of the 

 tissues must be thorough in order to get a sharply defined picture 

 of the nerves, since the combination of the methylene blue with 

 blood presents a diffuse, indistinct picture with poorly stained 

 nerves ; the nerves must be superficial or covered only by a thin 

 layer of tissue; the air must come in contact with the nerves, 

 otherwise no differentiation takes place. 



During the final stages of bleeding the anaesthetized animal 

 from the femoral arteries, a 2^0 per cent isotonic solution of 

 methylene blue "nach Ehrlich" at body temperature was injected 

 into both carotid arteries and continued until the injecting fluid 

 emanated perfectly clear from the femorals. A tourniquet was 

 then applied around the neck below the point of injection under 

 a pressure sufficiently low to insure filling of the cephalic vessels 

 without danger of diffusion or rupture. 



On account of the capricious character of this stain, litters of 

 very young puppies or kittens were injected at the same sitting, 

 so that the defects of some might be supplemented by better 

 staining of others. The total nerve supply then is a summation 

 of results, a reconstruction as it were. 



After a few minutes to allow penetration of the stain, the 

 skull was opened and a block of tissue, including the hypophysis 

 with its vessels and nerves in their normal relations, was removed 

 from the base of the brain. The hypophysis was gently retracted 

 so as to allow full exposure of one side to the air. The nerves 

 then assume their differential blue. These specimens were imme- 

 diately studied under the binocular microscope. The study of 

 fixed specimens with post mortem staining was far less satis- 

 factory, because of the collapse of blood vessels, with which the 

 ner\'es are intimately associated, the more stiffened picture, and 

 the deficient maintenance of the blue in the nerve fibers. 



