434 CHARLES R. STOCKARD AND E. M. VICAR] 



health. She was a most valuable matron bitch and had pro- 

 duced a record of fifty puppies within a period of two years. 

 Very probably this high fecundity, with the production and 

 nursing of litters of as many as fifteen puppies, may have 

 indirectly brought about the hyperthryoid picture, although 

 the appearance and behavior of the dog- when in good health 

 gave no evidence of such a condition. 



The high columnar follicular epithelium seen in the photo- 

 micrograph of this hyperactive thyroid gives the superficial 

 impression of abundant extrafollicular tissue. Closer exam- 

 ination of the section shows only a sparse amount of such 

 tissue, and the general pattern of this thyroid is closely the 

 same as that shown from 326 9 (pi. 82) which has large 

 follicles and little extrafollicular material. 



Figure 3 in plate 83 illustrates a thyroid section from 

 another female St. Bernard, 186 9 . This section differs from 

 the two already described in having larger follicles with 

 harder and more brittle colloid, giving the characteristic 

 appearance of a lower functional level. The general histologic 

 pattern in these three St. Bernard thyroids is closely the 

 same, and the widely different appearances in the photomicro- 

 graphs are due largely to the different states of activity 

 existing in these thyroids at the time of death. No such ex- 

 planation is applicable to the structural contrasts between 

 the follicular patterns in the thyroids of the shepherd and 

 St. Bernard and the Pekingese and Boston terrier (pi. 82). 

 The excessive amounts of extrafollicular tissue in the Peking- 

 ese and Boston terrier thyroids consist of both parafollicular 

 cells in groups of different sizes, and misplaced, irregularly 

 distributed epithelial cells resembling those in the follicular 

 wall and giving rise in many places to extrafollicular colloid. 

 The general follicular formation is not normally and per- 

 fectly expressed in the glands from the breeds with short 

 bulldog-like head shapes. 



Finally we may examine the microscopic structure of the 

 thyroid from two breeds of toy or midget dogs with almost 



