GENETIC TYPE AND THE ENDOCKIXKS 427 



The follicles in the bulldog thyroid are very much smaller 

 than normal, and are extremely variable and irregular in out- 

 line. The general picture is that of demoralization in follicu- 

 lar development, giving a somewhat adenomatoid character 

 to the gland. Yet it will be recalled that these glands of the 

 bulldog are of proportionally small size with no tumor-like 

 reaction involved. The general irregularity and defective 

 follicular formation result from early maldevelopment. In 

 spite of the irregular form and often confluent nature of the 

 follicles, the epithelium in many regions is high and very 

 active, as indicated by abundance of secretory droplets around 

 the periphery of the small colloidal masses within the ir- 

 regular follicles. Such follicular conditions might at first 

 sight give the impression of hyperactivity, but further study 

 shows this gland to be very different from the histologic 

 picture of the gland in common hyperthyroidism. The physiol- 

 ogy of the bulldog also refutes the idea of thyroid hyper- 

 activity. The basal metabolism is not high; the animal is 

 slow and inactive and inclined to become fat, although a com- 

 paratively small eater. The photomicrograph of the bulldog 

 thyroid shows an excessive amount of extrafollicular ma- 

 terial. Some of this consists of epithelial cells not properly 

 incorporated into follicles, and in some cases these cells seem 

 to give rise to colloid which lies outside and between the 

 follicles. However, there is no evidence of desquamation from 

 the follicular epithelium which Frey claims to be a constant 

 feature. The extrafollicular epithelial cells are not to be 

 confused with the so-called parafollicular cells. The latter 

 do not give rise to colloid and, in the dog, respond specifically, 

 as Nonidez has found, to silver nitrate impregnation. Also 

 the typical parafollicular cells, so common in the thyroids of 

 most dog breeds, are practically absent from the English 

 bulldog thyroid and are, when present at all, very scarce, 

 as is shown by tests with the silver stain. 



There is frequent evidence of developmental arrests in 

 both the thyroid and parathyroids of the bulldog. We shall 



