^04 A.H. Estabrook 



actual, though shght, inhibition of growth due to the ^ NaCl. 

 Thus ii is on the border Hne between a strength that will and one 

 that will not affect growth in Paramecia. 



it and ^- NaCl in hay infusion. Neither of these concentra- 



4 5 -^ ' 



tions has any characteristic effect on the growth. See tables XII 

 and XIII. 



Role of Osmotic Pressure in Effects of Sodium Chloride 



We may now ask whether these effects of NaCl are due to the 

 osmotic piressure of the sodium chloride in solution acting on the 

 Paramecia, or to the direct chemical effects of the substance, or 

 to both. 



By means of freezing point determinations,^ we find that the 

 osmotic pressure of ordinary hay infusion is .44 atmospheres. 

 In table XIV is given the osmotic pressure of the different solu- 

 tions of sodium chloride which we have used. 



By examination of the table we find that an increase in the 

 osmotic pressure from .44 atmospheres (that of hay infusion), 

 to 1. 841 atmoshperes (that of ^ NaCl in hay infusion), has only 

 a shght effect on the growth. Growth that was almost normal 

 took place in ^ NaCl in hay infusion. But when we increase to 

 an osmotic pressure of 2.528 atmospheres, that of ^ NaCl in 

 hay infusion, there is a marked effect on the growth, which is 

 even more marked at the pressure of 4.546 (that of^^ NaCl.) 

 This would seem to indicate then that an increase in osmotic 

 pressure had an injurious effect on growing Paramecia. To give 



5 The osmotic pressure of the hay infusion has been found by the loweringof the freezing pointmethod. 

 When the lowering of the freezing point has been determined by the Beckman apparatus, the osmotic 

 pressure is computed from the following forumula: 



O. P. = A X ^ 



1.86° 



Where A is the lowering of the freezing point, 22.3 is the osmotic pressure of a weight normal solution, 

 and 1.86° is the loweringof the freezing point caused by a weight normal solution- The freezing point 

 of a sample of hay infusion such as was known to be favorable to the growth of Paramecium was found 

 to be .036 below that of pure distilled water, and by applying the above forumla the osmotic pressure of 

 the hay infusion was .44 atmospheres. 



