PROSSER 



HANNON: In our own work we have found a decrease in both 

 liver and muscle after one month of acclimatization. Other people 

 who have acclimatized their animals for a much longer period 

 find no change in the system. This brings up another question: A 

 number of investigators, includingsome of the workers at Dr. Hart's 

 laboratory, Heroux in particular, have found that the liver metabol- 

 ism of animals that are subjected to seasonal, outdoor acclimatiza- 

 tion is the same in both summer and winter. Along similar lines, 

 we have found that liver metabolism varies with the duration of expo- 

 sure. It goes through a peak— in our particular circumstances at 

 one month— and then it falls back to the normal levels. It would 

 appear then, that the initial response to alow temperature, at least 

 in this organ, is an increase in metabolism per unit mass of tissue. 

 With longer exposure, however, we find an increase in the rela- 

 tive size of the liver. Metabolic ally, this increase in mass replaces 

 the increase in unit activity, and theliverthus retains a high meta- 

 bolic rate by virtue of its size.Inotice in your data that practically 

 all of the metabolic rates are expressed as oxygen consumption per 

 gram of tissue, and there is no indication of whether the relative 

 mass of tissue has changed. You do have evidence that the protein 

 content does change, but I would like to ask whether there were any 

 changes in relative liver mass comparable to those we have observed 

 in rats. 



PROSSER: Dr. Murphy has found the changes in liver size and 

 in the same direction that you find them. That is, the liver of a 

 goldfish that has been held at 30 C is very small, whereas the one 

 that has been held at 5 C is large. We thought it has more fat on 

 a unit weight basis. It does not. It has less fat. You are finding 

 that the fatty acid metabolism increases, are you not? 



HANNON: Yes, but we have studiedonly the liver. Dr. Depocas, 

 I believe, has found that the intact animal can oxidize fatty acid 

 at greater rates in the cold. Am I correct, Dr. Hart? 



HART: Yes, but not associated with acclimation. There is a 

 greater elevation of oxidation in the cold, but there was no change 

 associated with acclimation. 



40 



