448 



BULLETIN OF THE BUREAU OF FISHERIES. 



While tumor fish not infrequently have blood infections, plates made from the heart 

 blood of several of these tumor fish remained sterile, save in one case. The hemoglobin 

 readings and other data for each individual are given in the following table : 



TABLE VI. HEMOGLOBIN ESTIMATIONS ON THE BLOOD OF TROUT AT THE STATE HATCHERY AT 



PARIS, MICH., IN OCTOBER, 1902. 



Average 37.5. 



6 Average 21.6. 



SPONTANEOUS RECOVERY. 



In the microscopic examination of sections of carcinoma of the thyroid at Craig 

 Brook station during the summer of 1909, we occasionally encountered what appeared 

 to us to be evidences of regression in certain tumors. We therefore were led to look 

 for evidences of spontaneous recovery. To determine whether a change to more favor- 

 able conditions on the part of the fish would increase the number of spontaneous recov- 

 eries, in the autumn of 1909, 119 fish with visible tumors, mostly of large size, were 

 selected from a lot of landlocked salmon (lot 1950), and placed in pond i at Craig 

 Brook station. During the winter of 1909-10 two yearling brook trout with small 

 thyroid tumors visible at the isthmus were held without food in a glass jar in the cold 

 with occasional changes of water. One died after a few weeks with the tumor still 

 visible. During 44 days the tumor of the other fish disappeared entirely, leaving the 

 entire thyroid region without external enlargement. In the early spring' of 1910 an 

 examination of the 119 tumor-bearing fish in pond i was made to determine to what 

 extent spontaneous recovery might have affected this advanced lot. The conditions 

 in the pond were more favorable than in the pond below. Here the fish received pure 

 water directly from a spring, had access to natural vegetation, and obtained from their 

 surroundings some natural food while they were fed very little artificial food. Thus 

 they were in a large degree removed from fish culture. During a year the loss was 

 67 per cent and of the remaining fish only 56 per cent showed visible tumors. 



