Experiments on the Early Development of the Amphibian Embryo etc. 639 



They were allowed to remain in this very weak solution for 

 24 hours. At which time the solution was poured off and replaced 

 by one of double the strength (0.1%)- Subsequently every 24 hours 

 the strength of the solution was increased 0.1% iiiitil it reached 1%. 

 All the eggs developed normally without any indication of the free 

 yolk plug. Some of the Chorophilus eggs hatched out in four days, 

 when the solution had a strength of 0.3 They lived until the 

 reserve food material of the yolk was used up, when they all died, 

 having refused any other food. The last one died on the 10*^ day 

 when the solution had a strength of 0.9%. 



The Rana eggs hatched in 7 days (0.6% ^ol-) some of them 

 lived for 6 days afterward, when the few that remained were pre- 

 served for examination. 



The Amblystoma eggs did not hatch until the 12^^ day, and 

 then lived 4 or 5 days longer in a 1% solution. 



We thus have embryos living and swimming about freely in a 

 solution of sufficient strength to kill them if they had been placed 

 in it immediately. 



We know from our own experiments that the influence of the 

 salt solution is negatively, rather than positively injourious i. e. it 

 does not directly injure the protoplasm but simply hinders or pre- 

 vents it from performing its normal function. This preventive in- 

 fluence has more effect upon the protoplasm than upon the nucleus 

 and when it becomes sufficiently strong to overcome the functional 

 activity of the latter the organism dies. 



The present experiment teaches that the ability of both nucleus 

 and protoplasm to withstand this influence in any particular case is 

 capable of education and can be increased by being gradually exer- 

 cised. This development can be carried so far as to enable the 

 organism to easily overcome influences that would otherwise quickly 

 prove fatal. There seems to be differences between the three species 

 in their capacity for such development. In ordinary life many ad- 

 verse influences, such as stagnation of the water or the presence of 

 any salt or mineral in solution, come on gradually, and this capacity 

 on the part of the embryo for increasing its ability to withstand such 

 influences must prove of great service, and often times prevent a 

 fatal issue. 



In reviewing the teaching of these experiments the first general 

 fact which they indicate is that »the extraordinary delicacy with 

 which the frog's eggs respond to slight variations in the surrounding 



