PETERS. — METABOLISM AND DIVISION IN PROTOZOA. 513 



Stentor at that time, owing to the acidity of the medium. When the 

 initial fermentation has ceased the acidity diminishes and Stentors 

 multiply. 



3. Division in Stentor can be both accelerated and modified in char- 

 acter by the presence of an excess of potassic chloride in an otherwise 

 normal medium. In Paramaecium an acceleration which is normal in 

 character occurs under the influence of a small proportion of chloroform 

 in an otherwise natural medium. 



4. The effects on the division of Stentor produced by the chlorides of 

 calcium, potassium, and magnesium are represented by the curves given 

 on p. 473. Each curve taken by itself shows the effect of the factor of 

 concentration. Secondary curves connecting experiments at the same 

 osmotic concentration (see explanation of curves, p. 466) make an angle 

 with the axis of abscissas ; that is, they show that the salts have specific 

 effects in addition to their osmotic activities. Milk sugar at concentra- 

 tions equal to or greater than those used with the above four salts is 

 harmless for Stentor. This fact shows that abstraction of water was not 

 a prominent factor in the action of the four salts. Excessive proportion 

 of a single salt was the destructive factor. Measurement of conductivity 

 shows that distilled water kills Stentors by abstraction of salts. At 

 extremel}* high concentrations sugar, as well as salts, kills cells, partly 

 at least by abstraction of water. 



In regions of the concentration curve extending between these ex- 

 tremes the effects of different concentrations do not differ sharply, as 

 shown, for example, by the curve for calcic chloride. Hence the theo- 

 retical concentration curve for a single salt has a more or less broad 

 elevation in its middle, or isotonic, region and descending limbs towards 

 both hyperisotonic and hypisotonic extremes. 



5. The permeability of the cell membrane is altered by distilled water, 

 probably being increased by it. In milk sugar it probably remains 

 normal. The effect of salts upon the permeability of the cell is a highly 

 important factor in their action on free-living cells. 



6. The curves on page 473 show different degrees of adjustment of 

 Stentor to the chlorides of calcium, potassium, sodium, and magnesium in 

 the order named. 



7. A combination of several physiological salts results in a more 

 favorable adjustment than a medium containing only one. 



8. Stentor is well adjusted to a medium composed of calcic chloride 

 + sodic nitrate + magnesic sulphate + di-potassic phosphate in given 

 proportions. 



vol. xxxix. — 33 



