402 CHARLES I!. STOCKARD AND E. Rl. VICAEI 



amount of thyroid tissue in milligrams in proportion to 

 kilograms of total body weighl was calculated. Comparisons 

 based on such calculations are, of course, not absolutely exact, 

 and no account is taken of the occasional additional posterior 

 thyroid material which, in the presence of the two usual 

 thyroid lobes, is very insignificant. As is well known for 

 several mammals, with particular reference to the studies 

 by Brown ( '29) on rabbits, there is great variation in relative 

 thyroid size among perfectly normal individuals of the same 

 breed. This individual variation is constantly found among 

 the members of the several dog breeds which we have studied. 

 Unless the proportion of thyroid material to body size were 

 to differ very much more in two different breeds than among 

 the members of a single breed, this quantitative variable 

 could, of course, have no significant effect on the determina- 

 tion of physical type or functional pattern. 



In order to analyze the thyroid proportions, we may first 

 consider the individual differences in relative size found 

 among the members of each of several pure breeds. Text- 

 figure 79 indicates the amount of thyroid in milligrams per 

 kilogram of body weight for the dachshund and Boston 

 terrier, two partially dwarf breeds of strongly contrasted 

 type. Text-figure 80 shows the same for the bassethound and 

 English bulldog, both of normal canine size; and text-figure 

 SI gives relative weights for the great Dane and the St. 

 Bernard, dogs of gigantic proportions. 



The proportional sizes in milligrams of thyroid material 

 to kilogram of body weight in the six adult Boston terrier 

 females represented in text-figure 79 give the series 90-100- 

 120-130-150-210, and the largest proportion of thyroid is 

 2^ times greater than the smallest. The adjacent series of 

 bars represents the proportional amounts of thyroid in seven 

 adult dachshund bitches. The lowest of these is 100 milli- 

 grams per kilogram and the highest 320; the latter dog is 

 therefore 3.2 times richer in thyroid material than the former. 

 The other five individuals grade quite regularly between 

 these two extremes. These figures indicate that the propor- 



