CARCINOMA OF THE THYROID IN SALMONOID FISHES. 447 



that for recruits who have reached the age for military service for the district, 9.22 

 per cent. From this it would appear that there is a steady increase of goiter in school 

 children up to the age of puberty, with a marked decrease between that age and 20. 



Our tables show that for brook trout yearling fish the maximum is 28 per cent, 

 .or 2-year-olds 65 per cent, and for fish older than 2 years 91 per cent. It may be 

 stated for brook trout in captivity that a large proportion of them at least have acquired 

 their reproductive faculties in the second year and that their full reproductive faculties 

 are certainly acquired by the third season. It thus appears from our figures that fish 

 exhibit a very high, probably the highest, incidence in the period from 2 to 5 years, 

 which in the life of a fish carries it well beyond the comparable period in human beings. 

 We have frequently met with instances of actively growing tumors in the oldest fish 

 under observation and the large tumors in old fish have never presented an appearance 

 comparable to colloid goiter. So far as this comparison is admissible it would indicate 

 that the process in the fish in its age incidence is more in accord with McCarrison's 

 observations than the Bavarian statistics just quoted. Both McCarrison's statistics 

 for man in Chitral and Gilgit and our own for fish reach well into the period of increasing 

 incidence of neoplasms in mammals. 



HEMOGLOBIN ESTIMATIONS. 



In the autumn of 1902, before thyroid carcinoma in fishes had attracted attention 

 in this country, one of us observed, incidental to work upon bacterial infection in trout, 

 an anemic condition among a certain lot of brook trout at a State hatchery at Paris, 

 Mich. These fish were i^ years old and were part of a lot of several hundred which 

 had been sorted and segregated from the general hatchery stock on account of their 

 undersized and stunted condition. Except for their small size this lot was in fair 

 condition and most of them would have spawned for the first time some weeks subse- 

 quent to these observations. Of this selected lot the percentage having tumors was 

 not determined but there were more normal healthy fish than those bearing tumors. 

 Even the tumor fish with anemia showed no particular emaciation or falling off in 

 condition. 



Nine apparently healthy fish without tumors were taken at random from this lot 

 and hemoglobin readings obtained. Nineteen tumor fish from the same lot then had 

 their hemoglobin estimated in the same way. The range of the former was from 30 to 

 43, of the latter from almost nothing 1047, the averages being 37.5 and 21.6, respectively. 

 The readings were made with a Dare hemoglobinometer; those recorded as 8 are arbi- 

 trarily overstated, the samples scarcely showing red and registering much below the 

 lowest scale reading. The fish showing the highest reading (47) had only a very small 

 tumor, in the jugular pit. The largest fish of the series (first of the table) showed one 

 of the lowest readings, and had marked blood changes. The tumors were not measured 

 or accurately compared, but the larger usually gave the lowest readings. A marked 

 poikilocytosis accompanied a low blood count for red cells. The normal red cells 

 numbered 256,000 per cubic millimeter, or 416,000 including the atypical reds of extra- 

 ordinarily small size. The red cells of normal brook trout blood number about i ,000,000 

 per cubic millimeter. 



