5o8 A.H. Estabrook 



to grow in these solutions, which have a large amount of the chem- 

 ical present in them, is probably due as much to the extraction 

 of water from the cells as to the direct action of the chemical upon 

 the life activities. 



Comparative Resistance of Adult and Toung Paramecia to ^-^ NaCl 



Early in the work it was noticed that adult Paramecia put into 

 a -|^ NaCl solution continued to live, the solution having appar- 

 ently no effect upon them, while young Paramecia put into the 

 solution just after division died, before the end of 30 hours (as set 

 forth above). A careful test of the varying resistance in the 

 two cases was made as follows: Into each of the two depressions 

 of a single slide was put a few drops of -^-^^ NaCl solution. Into 

 one was put an adult Paramecium, into the other a young one 

 from a fission just completed; both the adult and the young 

 coming from the same stock culture, so that the past history 

 would be nearly the same. Thirty-two pairs such were arranged 

 and their further fate observed. The results are shown in Table 

 XVI. 



This experiment and other data given above (page 500), shows 

 that adult Paramecia may live normally and grow in a solution 

 that sooner or later kills Paramecia if they are put into the solution 

 just as the two halves separate at division. 



Are Paramecia in Stages Preparatory to Division Like Adult or 

 Like the Toting in their Resistance to the Salt? 



To test this the following experiment was tried: Paramecia 

 which were preparing for division were selected. They were 

 then grouped in pairs, those being put together which were in 

 the same stage of preparation for fiss on. (This is very easy to 

 do with much accuracy, since one accustomed to working with 

 Paramecia can tell within a few minutes when a dividing Para- 



