April, 1917] Tumors in Dogs 183 



Two of the four specimens studied by MuUer and Speese ('06), 

 had undergone carcinomatous change. The character of these 

 solid nodules is definitely carcinomatous. This specimen is, 

 therefore, to be classed as a cystocarcinoma papilliferum. 



SUMMARY. 



These enlargements of the thyroid gland are all due to a 

 new growth of the glandular epithelium. The cells of this new 

 growth do not present the differentiation typical of thyroid 

 epithelium. They have lost for the most part their polarity and 

 normal arrangement. In certain instances these losses are so 

 marked that from individual sections it could not be ascertained 

 that the tissue was at all related to the thyroid gland. All 

 gradations between this and definite tubules containing colloid 

 are observed. The growths are not localized but have infiltrated 

 more or less the surrounding glandular structure. In the more 

 advanced cases, secondary nodules are found in distant parts, 

 particularly in the lungs. Since infiltration and metastasis are 

 late manifestations of most carcinomas, it is not surprising to 

 find that several of these tumors taken from dogs which were 

 apparently healthy should present secondary nodules and that 

 the infiltration seen in the specimens presenting only single 

 small nodule should not be as yet extensive. 



The incidence of malignancy in our series is somewhat higher 

 than in the human. In 5,000 goitre patients treated at the 

 Mayo Clinic, ('13), 52 carcinomas were found. It is to be 

 noted that this series of dogs, not selected but taken as they 

 came into the laboratory, and therefore, representing the 

 average healthy dogs of Columbus, present a malignancy 

 incidence nearly equal to that of the Mayo series of humans 

 selected because of diseased thyroid glands. In Ohio (1910- 

 1913), the mortality from goitre was 21.2 per 100,000 persons 

 living. Many of these were non-malignant diseases of the 

 gland since all fatal diseases of the thyroid are returned as 

 goitre. 



Because of the source of the material, the exact ages of the 

 dogs could not be determined except in one instance in which 

 by accident the dog was known to be twelve years old. All 

 the others, however, appeared to be old dogs as judged by the 

 general appearance and activity of the animals and the condi- 

 tion of their teeth. 



