2 INTEODUCTION. 



iind entblossen^/ Swammerdam made the earliest experiments on 

 the contraction of muscle by means of chemical and mechanical 

 stimulation of its nerves; thus laying- the basis of our present 

 nerve and muscle physiology^ which has been built up within rather 

 less than two hundred years ; thoug-h during the first half of this 

 period but little advance was made. 



From the famous September evening of the year 1786^ on which 

 Galvani first observed the twitchings of a frog^s leg suspended by a 

 metallic hook to an iron balcony, the frog has, down to the present 

 time, afforded almost the only material for the investigation of the 

 excitability of nerve and its associated electromotive changes, and also 

 no inconsiderable part of the remaining nerve and muscle physiology. 

 It was not until Mûller devised the method of operating on the 

 frog that BelFs law became capable of easy proof ; and much of 

 our knowledge of the functions of the spinal cord is derived from 

 experiment upon it. Again, the muscles of frogs served, from the 

 time of Swammerdam to that of Eduard Weber and his followers, 

 for the investigation of the phenomena and the conditions of con- 

 traction ; and in almost all other branches of physiology there are 

 important doctrines which were first definitely established by experi- 

 ment upon the frog. But for the web of the foot of this animal (and 

 the gills and tail of its tadpole, in which Leeuwenhoek ^ describes 

 the phenomena most clearly) we shovdd not, perhaps for a long 

 time, have arrived at a satisfactory knowledge of the existence 

 and the conditions of the capillary circulation. As is well known, 

 an accurate acquaintance with the constituents of the blood directly 

 concerned in nutrition has been obtained by observation on the 

 frog, as well as important facts in the physiology of the blood and 

 lymph, such as the intimate knowledge of the corpuscles of both 

 fluids, and the coagulability of the plasma ; while in no less degree 

 have experiments on these animals served to establish the laws of 

 "the hearths action. Moreover, physiology is not the only science 

 indebted to the frog : in histology many important results have 

 been obtained from observations on it, and for histological in- 

 struction it is now indispensable. To it we owe much of our 



' ' In animals witli warm blood the action of the muscles is neither so apparent 

 nor so long continued as in those animals which have cold blood, such as fishes and 

 many other aquatic animals, and those also which live both in water and on dry- 

 land. On this account I have made my investigations chiefly on frogs, for in them 

 the nerves are very distinct, and are easily found and exposed.' Buch der Natur, 

 Leipzig, 1752, p. 330. 



'^ Leeuwenhoek, Arcana Naturre III, epist. 65 ad Reg. Soc. Lond., p. 15S. 



