150 THE INFLUENCE OF INANIMATE SURROUNDINGS. 



that is, on the whole, injuriotis to the frog, I made a variety 

 of experiments in the following manner. To prevent the 

 creature from swallowing, and so dying of suffocation, I tied 

 it to weighted sticks in such a way that it was unable to dip 

 its nose and mouth into the water, even when its head began 

 to sink from weakness of the muscles. A great number of 

 frogs were placed in different vessels, each containing the same 

 quantity of water with various, but known, amounts of salt in 

 solution ; death was assumed to have taken place when the eye- 

 lids of the frogs no longer reacted under irritation, and did not 

 recover their sensibility after the creature was taken out of the 

 salt water and washed in fresh water. By this I found that a 

 frog commonly died, on an average, in about two hours and a 

 half in a solution of five per cent, of salt, in three hours in 

 three and a half per cent., in almost seven hours in two per cent., 

 and not before more than twenty-four hours had elapsed in one 

 and a half per cent. They all, without exception, endured a solu- 

 tion of one per cent, without sustaining any injury ; that is to say, ' 

 they lived as long in their very uncomfortable position as other 

 frogs which were fastened up in the same way in pure fresh 

 water namely, from three to four days. It remains still doubt- 

 ful, therefore, whether a frog cannot really live just as well in 

 water with one per cent, of salt in it as in fresh water. I have 

 not made any experiments on this point. But near Greifswald, 

 on the Baltic, frogs live and spawn, as I have learned from my 

 assistant, Dr. Braun; so it is highly probable that a solu- 

 tion of one per cent, of salt in the water is about the limit of 

 where it begins to be injurious to frogs. Similar experiments 

 have been made by Plateau on aquatic Articulata, and he seems 

 not to entertain the slightest doubt that in this case also the 

 salt penetrates through the skin ; although, when the animalls 

 are completely immersed in the water, imbibition through tfoe 

 mouth does not seem to be excluded. But as aquatic Articulata, 

 cannot die of suffocation so long as the water contains a suffi- 

 cient quantity of air, or as the animal is allowed to rise to the 

 surface to breathe, this question is of no practical importance to 

 us. The most important result established by the above-men- 

 tioned experiments, and by Plateau's, is this : that the behaviour 



