REGNARD'S EXPERIMENTS 191 



even inconsiderable differences in the environment, 

 when sudden, are accompanied with great danger to 

 the life of animals, while slow change may do no 

 harm at all ; it even happens that the adaptation of 

 the animal to the new environment becomes so close 

 that sudden transfer to the formerly normal one is 

 dangerous and even deadly. Instances of sudden 

 changes of any sort where the result is death are to be 

 met with in nature ; so that in all experiments bear- 

 ing on the influence of environment upon organisms, 

 care must be taken to alter it very gradually. Of course 

 there are great differences in this influence of environ- 

 ment on life ; any amount of carbonate or of sulphate 

 of lime, for instance may be added to water in which 

 tadpoles are living, without any injury ; other reagents 

 are not equally dangerous, for a number of reasons 

 which it is needless to enumerate here. 



Generally speaking, then, care must be taken to 

 alter environment slowly, if we wish to appreciate its 

 influence on organic forms and life. In some cases it 

 happens that, while not totally impairing life, a change 

 of environment is conducive to considerable change in 

 the vital functions. Such 1 Regnard has seen to be the 

 case in the animals subjected to pressures much 

 greater than that under which they commonly live. 



1 Cf. P. Regnard, Recherches experimentales sur les Conditions 

 Physiqtusde la Vie sous les Eaux . Paris, 1891. 



