GENETIC TYPE AND THE ENDOCMXES 423 



specific method to show the parafollicular cells. The right 

 suprarenal was placed in 15% formalin for frozen sectioning 

 and fat staining. The left suprarenal was divided, half being 

 fixed in Bouin's fluid, the other half in Zenker's, Helly's or 

 Susa's. 



The fixative giving the most consistently reliable results 

 for the pituitary was a modified Helly's fluid. Staining was 

 most satisfactory with a modified form of Mallory's triple 

 stain. 



The thyroids and suprarenals were usually sectioned at 

 seven microns thickness. Thyroids (including the internal 

 parathyroids) were sectioned as thin as five or six microns. 

 Some abnormal parathyroids were cut as thin as four or five 

 microns in order to study nuclear details. Serial sections were 

 made of the parathyroids, and special regions of the thyroid 

 glands. The pituitaries were cut in serial sections through 

 comparable regions at a thickness of four or five microns. 



The stains most often used were Mann's hematoxylin-eosin 

 (or erythrosin) and Mallory's triple stain. Heidenhain's 

 iron-hematoxylin and eosin were frequently used for detecting 

 nuclear types in the parathyroids. As supplement to the 

 Mallory triple stain, the special stains of Altman and Masson 

 were also used for the pituitary. 



Survey of histologic modifications in the thyroid. The 

 thyroid gland shows the most easily recognized histologic 

 modifications to be found among the endocrines in the dif- 

 ferent breeds of dogs. For this reason its histology will be 

 considered first, in order to give the general plan of analysis 

 for determining what relationship if any is to be found be- 

 tween endocrinic modifications and the peculiar structural 

 and functional characteristics of the dog breeds. 



Plates 81, 82 and 83 show photomicrographs from typical 

 sections of thyroids. Plates 81 and 82 have been arranged 

 so as to show sections from the short muzzled bulldog-like 

 breeds at the top and long muzzled, more nearly normal 

 canine types at the bottom. This arrangement facilitates 



