PETERS. — METABOLISM AND DIVISION IN PROTOZOA. 505 



The medium here used consisted of the following salts dissolved in 

 ordinary distilled water. 



NaoHPO^ 00030 m. 



KNO3 00010 m. 



FegCIe trace 



In this case the concentration would of course be much higher. De- 

 terminations, as made in the next experiment, of the concentration 

 of mass-cultures gave a range equivalent to that of a 0.00100 m. to 

 0.00200 m. calcic chloride solution. Without doubt Stentors taken from 

 any of my mass-cultures and placed in the above test-medium made 

 with distilled water would suflTer a change from higher osmotic concen- 

 tration to lower, that is, this medium presents for them hy|)isotonic con- 

 ditions. "Within the cell there exist unbalanced partial pressures of such 

 physiological salts or ions as are not represented by the medium. In 

 the latter di-sodic phosphate is probably present in a concentration that 

 exceeds the amount of the same salt normally contained within the cell. 

 In consequence of the unbalanced partial pressures on both sides there 

 ensues a double movement of salts or ions, if the membrane is perme- 

 able to them. Since the medium is hypisotouic to the cell, there is 

 also an inward movement of water tending to produce an increase of 

 volume in the cells. The total result of all these processes is to 

 increase the conductivity of the medium. This result signijies an in- 

 creased concentration of salts. It does not follow directly that the mem- 

 brane is permeable to the salts in question. The case is different from 

 that of pure distilled water, where absorption of water from the medium 

 by the cell could not in itself increase the conductivity of the medium. 

 No possible loss from pure water could affect the conductivity of the 

 remainder, whereas any outward movement whatever of salts would 

 result in increased conductivity. But if in the present experiment, con- 

 ductivity having increased, it could be shown that the cells exhibited no 

 change in volume, then permeability would be demonstrated. Or if 

 from the increase in concentration of the medium there were subtracted 

 a correction, expressing the concentration-equivalent due to loss of water 

 from the medium to the cell, a remainder, if any, would measure the per- 

 meability. Such a correction, determined by the haematokrit method, 

 has been applied to chemical estimations in the case of blood corpuscles. 

 I have not attempted this method with Stentor, and to find a concentra- 

 tion-equivalent in terms of conductivity may not be feasible. Hence the 



