210 Relation of Nervous System to the Developing Musculature 



A few preliminary experiments with older larvre demonstrated that a 

 0.02 per cent solution, i. e., two parts of acetone-chloroform in ten 

 thousand parts of water is sufTicient to narcotize them completely/ and 

 that the action of the heart is not materially altered. Weaker solutions 

 do not completely inhibit muscnlar reflexes. Solutions of 0.04 per cent 

 and stronger seriously affect the circulation ahd ultimately cause death. 



After these facts had been determined, the experiments bearing upon 

 the problem to be solved were undertaken. Embryos of each species of 

 frog were placed in similar dishes containing water and solutions of the 

 drug of various known strengths, in order that their development in each 

 might be compared. The embryos selected were all in the same stage of 

 development (Fig. 1) and showed no trace of histological differentiation 

 in the nervous system or musculature. In each experiment care was 

 taken to keep the conditions influencing the different sets of embryos as 

 nearly uniform a:s possible, varying only the strength of the solution. 

 Owing to the volatility of acetone-chloroform, it was found necessary 

 to keep the dishes containing the embryos closed, and to change the fluid 

 every day or two. 



Several factors which had a district influence on the success of the 

 experiments manifested themselves during their course. It was found, 

 in the first place, that the embryos of E. virescens suffer least from the 

 •action of the drug. Those of E. palustris are somewhat more susceptible, 

 while sylvatica embryos exhibit a considerably more marked tendency 

 towards deformity. Again, it was found that the deleterious effects of 

 the drug were less marked when the temperature was near the optimum 

 for development, for this permitted the embryos to reach the final stages 

 of development in a minimum time. 



The results of the experiments may be summed up very briefly. The 

 embryonic development takes place in solutions of the drug, when care 

 is taken to keep the conditions favorable, in an almost normal manner, 

 although distinctly more slowly than in water. The retardation of the 

 development is directly proportional to the strength of the solution. The 

 results in detail may best be presented by giving the original record of a 

 typical experiment. 



Experiment 6. 



April 20, 1902. Sixteen palustris and seven virescens embryos are put into 

 a 0.03 per cent solution of acetone-chloroform, and eight palustris and three 



" There is some discrepancy between this result and Miss Randolph's, who 

 makes the minimal dose much stronger. This can perhaps be explained by 

 the rapid volatilization of the substance when kept in open vessels. 



