STUDIES ON THE PANCREAS OF THE GUINEA PIG 307 



solution kept fluid by the addition of 10 per cent of potassium iodide. 

 When the injection is complete inject, by a cannula tied in the 

 pancreatic duct, a 5 per cent solution of ammonium molybdate. 

 This precipitates the gelatine and at the same time fixes the janus 

 green. Pieces of the pancreas are then washed as rapidly as pos- 

 sible with cold water to get rid of the ammonium molybdate, 

 then quickly dehydrated with absolute alcohol, cleared in toluol, 

 and mounted in balsam. During the dehydration the safranin 

 resulting from the reduction of the janus green is extracted, and 

 the resulting preparation shows slate blue islets clearly outlined 

 and defined, but so transparent that with a binocular microscope, 

 one can follow every blood vessel in them. No section cutting 

 is necessary for the pancreas of the guinea pig or that of the rabbit. 

 The latter in particular, on account of the thinness of the lobules, 

 is well adapted for this kind of preparation. Double injections 

 have also been made by this method, but offer no advantages 

 over the injection of a single color-mass. 



Jj.. Methods of fixation 



a. Lane's metJiods for deriionstration of the A cells of the islets 

 of Langerhans: 



A. Fix the tissue for two to four hours in: 

 Saturated alcoholic solution of mercuric chloride, 



Two and one-half per cent solution of potassium bichromate; equal parts. 

 Wash in 50 per cent alcohol; then pass through graded alcohols to absolute; etc. 

 Sections 3 micra thick are stained in neutral gentian (see below). 



B. Fix the tissue in alcohol 70 per cent. Stain sections in neutral gentian 

 (see below). 



6. Lane's rnethodfor the demonstration of the B cells of the islets 

 of Langerhans: 



Fix in the following solution four to twenty-four hourK: 



Potassium bichromate 2.5 grams 



Mercuric chloride, 5.0 grams 



Distilled water 100.0 cc. 



Stain in neutral gentian (see below). 



