234 ANIMAL AGGREGATIONS 



The difference, 2.72 hours, has a statistical probabiUty of 0.0564, 

 which is too great for much significance to be attached to the ob- 

 served difference. These values are to be compared wi^i the results 

 shown in Table XXV, which were obtained immediately preceding 

 the present experiment. That test showed a difference in survival 

 of 10.65 hours, with a probability of 0.00002. 



When comparison is made between the survival in the charcoal- 

 treated medium and the less-dilute sea-water which had an initial 

 resistivity of 5,050 ohms, the difference in survival time is 2.53 hours, 

 with a statistical probabihty of 0.072. These values are to be com- 

 pared with a survival difference of 6.55 hours and a probability of 

 0.02 in the preceding experiment with the same type of culture 

 water similarly dialyzed but not treated with charcoal. 



These results indicate that the charcoal did remove a part of the 

 actively protective substance, and suggests the need of further work 

 at this point. Perhaps more extended adsorption would have a still 

 greater effect. Another possibility must be mentioned, although 

 here, too, the evidence available at the present time does not warrant 

 the drawing of definite conclusions. I refer to the possibility of the 

 differential leaching of materials in raw and in biologically condi- 

 tioned water. Early in the analysis of the results here summarized, 

 indications appeared that worms isolated into water conditioned by 

 living organisms tended to lose electrolytes less rapidly than did 

 their controls isolated into hypotonic sea-water with the same initial 

 resistance. Accordingly, the resistance records were examined for 

 comparable experiments. The different exposures were for varying 

 lengths of time, and hence show a marked variation in the change 

 in resistance from that given at the beginning of the experiment. 

 The initial resistance of the observed solutions stood at different 

 levels in the various experiments, but always at the same level in 

 both the experiment and the control for any given experiment. The 

 mean difference in the whole series of experiments shows that there 

 was 4.8 per cent less change in the resistivity of the biologically 

 conditioned media than in their accompanying hypotonic sea-water 

 controls. Despite the many known elements of variation, this has 

 a statistical probability of 0.00068. 



