420 CHARLES R. STOCKARD AND E. M. YICAR1 



The charts representing pituitary amounts per kilogram 

 of body weight for the dachshund-Boston terrier cross, the 

 bassethound-English bulldog cross, and the great Dane-St. 

 Bernard cross, all fail to show recognizable correlation be- 

 tween gross pituitary proportion and pronounced structural 

 distortions. This fact again leaves us free to interpret any 

 relation between histologic quality and type characteristics 

 without reference to variations in pituitary amounts. 



The preliminary survey of the variations in gross propor- 

 tions of the thyroid and pituitary glands leads to the con- 

 sideration of the differences in histologic qualities of these 

 and other endocrine glands from dog breeds of contrasted 

 types in order to determine the possible significance of such 

 differences in relation to the enormous deviations from the 

 standard structural and functional type. 



Differences in the Histologic Qualities of Thyroid 

 Glands from Dogs of Pure Breed 



Introductory view. It is well known that each of the 

 endocrine glands exerts some rather specific influence over 

 the structural and functional reactions within the mammalian 

 body. It is also generally recognized that the action of any 

 one endocrine gland is not entirely independent of the in- 

 fluences of several or perhaps all other glands. The inter- 

 actions of the thyroid and pituitary in influencing the gonadal 

 functions is a well known example. There is, of course, a 

 general interaction and dependence in functional relation 

 among all the different organs and tissues of the animal 

 body, but the interrelation among the members of the endo- 

 crine system is much more definite and specific. It has also 

 been clearly established that most of the important altera- 

 tions in endocrine gland function result from or are accom- 

 panied by definite modifications in the normal histologic 

 patterns of the gland. Finally, it is now becoming widely 

 recognized that severe and chronic illness and disturbed ali- 

 mentary functions bring about various modifications in endo- 



