6 DUBLIN UNIVERSITY 



Bobert M'Donnell, M.D., M.B.I.A., Lecturer on Physiology in 

 the Carmichael School of Medicine, Dublin, read — 



NOTES OF SOME EXPERIMENTS REGARDING THE INFLUENCE OF PHYSICAL 

 AGENTS ON THE DEVELOPMENT OF THE TADPOLE OF THE COMMON FROG. 



For several successive years I have studied experimentally the influence 

 of physical agents upon the development of the tadpole of the common 

 frog. During the spring and summer of 1858 the experiments were 

 performed, of which an account is given in the following pages. 



At that time, and indeed until very lately, I was unacquainted with 

 the observations of John Higginbottom, F.B.C.S.,* on this subject, 

 which both he and I seem to have been led to investigate ; in order to 

 test the truth of an opinion very generally held by physiologists, that the 

 tadpole of the frog, when deprived of the influence of light, cannot arrive 

 at its full development and become a perfect frog. This opinion was 

 due, I conceive, to the assertions made by W. F. Edwards in his well- 

 known work, " De 1' Influence des Agents Physiques sur la vie ;" asser- 

 tions, the truth of which, I regret to say, I have found great reason to 

 doubt. 



April 19th, 1858. — First Experiment. — Two glass jars, cylindrical 

 in form, each 1 foot high, 5 inches wide, and capable of containing more 

 than half a gallon of water, were filled with fresh water ; 100 tadpoles, 

 many, but not all of which, had just lost the external branchiae, were 

 placed in each jar, and a diaphragm of net so placed across each, that 

 the tadpoles cannot ascend higher than within two inches of the surface 

 of the water. One of these jars (A) was placed in the window, the other 

 (A'), in the inside of a large chest, which, when closed, was perfectly 

 dark ; no food was put in either. 



21st. Fifty-three of the tadpoles in A are dead; none dead in A'. 

 The dead ones having been taken away, and fresh water given to those 

 that remained, the diaphragm was replaced as before, and (A) again 

 placed in the window. A' was not interfered with. 



22nd (morning). All save four were found dead in A' ; these conti- 

 nually swim up to the diaphragm, and are small, having but just lost 

 the external branchiae. 



Those replaced with fresh water in A yesterday seem lively. 



* Philosopbical Transactions, 1850, page 431. 



