306 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



REPORT OF KXPERTMEIVTii* UPOIV THE AIVIITIAI. HEAT OF FISHES, 

 mADE AT PROVirvCETOU^IV, MASS., DURINO THE 8U1?II?IER OF 1S>9, 

 IIV COIV:VE«JTIOIV WITH OPERATIONS OF THE riVITED STATES 

 FISH COlUiniSSIOiX. 



By J. H. KIDDER, Surg^eon, IT. S. IVAVY. 



Sir : The investigation of the manifestation of animal heat by fishes, 

 with which you intrusted me last summer, having been brought to a 

 pause for the time being by the close of the Fish Commission's summer 

 work, I submit the following report of my experiments, so far as they 

 have gone, with a description of the instruments used and the mode of 

 observation. 



But little in the way of actual experiment relating to this interesting 

 question seems to have been done by other observers than those con- 

 nected with the Fish Commission, although numerous allusions to the 

 remarkable adaptability of fishes to extremes of temperature, and occa- 

 sional records of more or less incomplete experiments, are to be found 

 scattered through scientific literature. A complete bibliography of these 

 fragmentary notes would be voluminous and of questionable value, but 

 a short account of such observations as I have been able to find a record 

 of, either interesting in themselves or of incidental value as throwing 

 light upon the investigation, is appended to this report. 



So far as I have been able to learn, all of the observations made 

 hitherto upon the temperature of fishes have been confined to the intes- 

 tinal canal, the thermometer being passed into the rectum or oesophagus, 

 as is the usual practice in observations upon the body temperature of 

 mammals. But the conditions are by no means the same. The intesti- 

 nal canal of a fish is thin and scarcely muscular 5 the walls of the abdo- 

 men are also thin, and so sparingly vascular that no blood flows when 

 they are cut through; and consequently, always surrounded as they are 

 by water, against the chilling effect of which there is no sufficient pro- 

 tection, it is by no means in the rectum or stomach that we should 

 reasonably look for the body temperature of a fish. In point of fact, 

 the experiments to be hereinafter detailed show clearly enough that the 

 rectum temperature of a freshly-taken fish rarely exceeds that of the 

 water in which it swims by so much as a degree (Fahrenheit). So that 

 it may be quite safely taken as an index to the latter temperature when 

 there is no deep-sea thermometer at hand. 



Another point to be considered is the fact that the gills of most fishes 

 float freely in the surrounding water, and that all of the blood in each 

 individual nuist, in passing through these organs, be spread out so as to 

 expose the greatest possible surface to the chilling effect of the water 

 quite long enough to reduce it to the same temperature. 



From the low organization of fishes, and from the simplicity of their 

 digestive and circidatory functions, considered together with the fact 



