des^Agens Physiques sur la Vie, 297 



those of the large vessel, and not submersed in the river, 

 passed through their changes of form without the least 

 appearance of the phenomenon being retarded. The run- 

 ning waters of the Seine, , probably contained nutritious 

 matter, which the water periodically renewed was more 

 deficient in. 



Under circumstances of moderate nourishment and tempe- 

 rature, the tadpoles under water did not complete their 

 changes but in a very partial and protracted manner, while 

 the greater portion made no change. The great difference 

 in the circumstances of the experiments seems to have been 

 the access to the air of those which went through their 

 transformations as usual. Exclusion from light made no 

 difference in the results, and these were solely influenced 

 by occasional renewal of air from pulmonary respiration. 



These animals possessing a double respiration, cutaneous 

 and pulmonic, that is, absorbing air from the water around 

 them and inhaling it from the atmosphere on its surface, 

 renders these facts highly curious. Fish possess only the 

 means of aquatic respiration, and the influence of temperature 

 was tried upon them submersed in water deprived of its air 

 by previous boiling, the heat being varied from 0° to 40°. 

 The fish died quicker under these circumstances than the 

 frog species in the same situation ; but their lives were pro- 

 longed more in the descent of the thermometer than during 

 its elevation, as also occurred with the experiments on frogs 

 and salamanders; and, in both cases, the younger the ani- 

 mal, the less it could resist the higher temperatures. At 

 40° the young animals only survived about two minutes, and 

 the adults many more. 



Fish were also submersed in closed vessels of aerated 

 water, and, by varying the temperature and the quantities 

 of water, the duration of their lives was augmented in pro- 

 portion to the increased volume of the liquid, the tempera- 

 ture remaining the same ; but when these experiments were 

 conducted in open vessels, the contact with the atmosphere 

 altered the plienomena. At 20°, a small fish expired in four 

 hours ; and when the temperature was lowered to 10° or 12°, 

 the same sort of animal lived several days ; and when the 

 water was kept clean by being changed every twenty- four 

 hours,, the fish lived indefinitely. , ,i , , 



It is known that fish rise periodically ,tp, ilie isurface of the 

 waters to respire; and Dr. Edwards discovered that they 

 did so when they have. reduced the properties of the air di^ 



