PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 307 



that their blood itself is chilled by close proximity with the surrounding 

 water at least once in each circuit, and that thus the oxidation of the 

 blood, so important a source of animal heat in mammals, is quite neu- 

 tralized, we ought not to expect so great a difference in temperature 

 between the blood of a fish and the water in which it swims as obtains 

 between the blood of mammals and the surrounding medium, nor that 

 the limits within which its normal temperature must be confined should 

 be so narrow. 



And, while it is difficult to believe that the chemical changes neces- 

 sary to the nutrition, waste, and repair of the body of a fish, taken 

 together with its active muscular movements, can go on without the 

 evolution of a large amount of animal heat ; it is also plain that we are 

 not to expect to find the manifestation of this heat either in the intesti- 

 nal canal, a mere osmotic tube for the passage and absorption of the 

 food, scarcely vascular and barely separated from the surrounding water 

 by the thin bloodless walls of the abdomen ; nor in the arterial blood re- 

 turning from the gills, chilled down to the temperature of the water 

 with which it has just been in intimate contact. 



We should expect to find the blood of a fish at its warmest after hav- 

 ing been distributed to the substance of the body, having furnished the 

 material for nutrition, taken up the results of waste, and received the 

 heat developed by these processes and by the conversion of muscular 

 motion ; that is to say, in the heart and branchial artery. 



The experiments to be described have been tentative for the most 

 part, and accordingly temperatures have been taken in the rectum, the 

 stomach, various parts of the muscular tissue, the large venous trunks, 

 the cavity of the "thorax"* after opening the heart, the interior of the 

 heart and branchial artery, and the young fish in the ovary (of a dog- 

 fish). When the heart was large enough to admit the bulb of the ther- 

 mometer, the greatest differences between the temperatures of the fish 

 and of the surrounding water were found in that locality. 



INSTRUMENTS. 



The thermometers used in these experiments were made expressly for 

 the purpose by Mr. John Tagliabue, of No. 66 Fulton street, New York j 

 and have proved to be very satisfactory. They are fifteen in number, viz : 



1. Two long thermometers, graduated in fifths of a degree, and cover- 

 ing the range from 32° to 100° F., for use as standards. 



2. A set of five short thermometers, graduated in fifths, marking 10° 

 each, and covering all together the range from 40° to 90° F. 



3. A second set of six short thermometers, similar to those last named, 

 marking from 7° to 15° each, and covering the range from 30° to lOO^F. 



4. A short thermometer with the end carrying the bulb curved upon 



*The term "thorax" is used for conTenience' sake, as indicating the anterior part 

 of the body cavity, in the neighborhood of the heart. 



