PETERS. — METABOLISM AND DIVISION IN PROTOZOA. 475 



To facilitate comparison this experiment is summarized in the follow- 

 ing table : 



Milk Sugar. Isotonicity. 



.01250 m. .00750 m. NaCl 



.01500 m. .00900 m. NaCl 



.01750 m. .01050 m. NaCl 



.02000 m. .01200 m. NaCl 



.02500 m. .01500 m. NaCl 



.03000 m. .01800 m. NaCl 



NaCl. 



.00700 m. .01250 m. CioHjiOia 50 5 



Tiiese data on milk sugar do not seem to me to be sufficient to yield 

 any satisfactory conception of how the salts act upon the organism. I 

 have worked out only the higher range of tlie concentration curve, 

 whereas from a physiological point of view it is a lower range of concen- 

 trations that represents normal conditions and is therefore of especial 

 interest. From the logical standpoint the investigation might have begun 

 with the action of pure water. Perhaps by this method additional fac- 

 tors could have been introduced into the jthysico-chemical reaction chain 

 sooner than by beginning with higher concentrations. A few tests of 

 the reaction of S ten tor to ordinary distilled water and to various samples 

 of supposedly pure water were suggestive of a new and interesting phase 

 of the general problem treated of in this research. It was evident upon 

 preliminary analysis that the physico-chemical phase would have to be 

 worked out carefully before tlie biological aspect could be approached. 

 As a measure of the purity of water I adopted its electrical conductivity. 

 This is altogether the most delicate and practicable of the known methods 

 for the end in view. For the measurement of conductivity I adopted 

 the Nernst apparatus (Nernst, '94, and Maltby, '95). For details of the 

 construction and use of the apparatus, and for the preparation of water 

 for the.?e tests, I refer to the original articles and to the part of this 

 paper dealing with General Metliods and Technique (p. 444). 



I determined that the average conductivity of tlie ordinary distilled 

 water whicii I used was about k = 6.8 X 10"®, and I also prepared a 

 quantity of water whose conductivity was k = 0.9 to 1.0 X 10~^ An 

 estimation of the degree of parity these numbers represent and of the 

 probable nature and importance of the contaminations present are stated 

 or referred to in Kohlrausch u. Holborn ('98, pp. Ill ff). Suffice 

 it to say here that the purest water I used as a reagent for Stentor 



