1885.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 221 



to be derived. It is, therefore, of great importance to ascertain also the 

 exact bearing of temj)erature upon the work done. So far as we are 

 able to find this has never been done by direct measurement. Cyon 

 [loc. cit.) ascertained it by calculation; direct measurement was imi)os- 

 sible, according to the method which he used. 



In the two subjoined experiments the tem])erature of the feeding 

 fluids was ascertained by an extremely delicate thermometer, which was 

 inserted into the common outlet tube, situated between the lieart and 

 the supplying Mariotte's flasks. The intention being to keep within the 

 working limits of the temperature, the latter, in the two exjieriments, 

 varied from 3° to 20° C. To i^roduce a change in the temperature 

 of the nutrient fluids, the flasks were either surrounded with ice or 

 placed in a vessel containing hot water. 



As a general rule, it may be stated that the amount of work done by 

 the heart increases in direct i^roportion to the temperature of the circu- 

 lating medium up to a certain limit, in the same way as does also the 

 rate. But these two experiments show more than that. As will be 

 seen, one was made in February and the other in the month of May. 

 The highest temijerature used in the former was IS^ C, the rate being 

 46 j)er minute, the work done only 30 c. c. per minute. This was 

 by no means the greatest amount of work done during the entire ex- 

 periment; on the contrary, the maximum amount was obtained under 

 a temperature of 12° C, the rate being 35 per minute. This shows 

 the influence of the season upon the maximum limit of the work pro- 

 duced by temperature variations. This limit, in a winter animal, is 

 accordingly at about 12'=' 0. It is different with the rate, which, ap- 

 parently, was still on the increase at 18° C, and since this was the 

 highest temperature used in the experiment, its limit cannot be said to 

 liave been reached at all. The conclusion, therefore, to be derived from 

 this experiment is that the maximum limit of the rate and the maximum 

 limit of the work done by the heart of the terrapin do not necessarily 

 correspond to the same degree of temperature of the circulating medium ; 

 the latter is reached much sooner than the former. 



In the experiment made during the month of May the highest tem- 

 perature used was 20° C, and here we see that neither of the two 

 maximum limits have been reached under that temperature, but that, 

 on the contrary, they still move together. The rate is about half of 

 that in the February experiment under the same temperature, showing 

 that the same temperatures affect the heart of cold-blooded animals 

 differently in different seasons of the year, both as regards the rate as 

 well as the work done. The maximum limit of the work produced lies 

 much higher in spring animals than it does in winter animals. Thus, 

 the induence of the season, by a comjiarison of these two experiments, 

 is, 1 think, very well shown. 



The practical deductions to be drawn from these experiments must, 

 of course, be that a strict account of all variations of temperature of the 



