1919 Hurd; on Osmosis in Nei-eocystis 185 



holdfast end, and placed in large galvanized iron tubs painted on the 

 inside. The tubs were placed in a deep trough built for the purpose on 

 a shaded porch of the laboratory. A water faucet at one end and an out- 

 let pipe at the other provided a way of keeping the temperature low on 

 warm days by means of a stream of cold water flowing around the tubs. 

 Not more than fifteen small kelps were placed in each of the five tubs. The 

 tubs were emptied each evening and at once filled with water containing 

 by volume 1/28 more fresh water. It happened that the tubs contained 

 28 times the volume of a small two-quart bucket which was a convenient 

 measure of the increase in the amount of fresh water each 24 hours. 



Before extracting the juice from the kelps for the freezing point de- 

 terminations, the plants were washed three times in tap water to remove 

 the salt water adhering to them, dried as well as possible by first wiping 

 all surfaces with cheesecloth, then left spread out on cloths for twenty 

 minutes. Any moisture left on the surface of the stipes or fronds pro- 

 duced an error in the freezing point reading. The fresh water, which of 

 course cannot be all removed, dilutes the juice, as does some absorption of 

 the fresh water during the washing. But at least the error is approxi- 

 mately the same for each extraction, whereas, if they were ground up 

 unwashed, the salt left on the surfaces would cause too high a concentra- 

 tion of the extracted juice and the error would not be the same for all 

 because the plants would come from waters of varying salinity. 



After washing and drying them, the fronds, stipes and bulbs were 

 ground up as finely as possible in an ordinary meat grinder. It was found 

 more convenient to use the juice from this joulp than to use the pulp for 

 the determinations. So the juice was squeezed out by means of a clean 

 cheesecloth bag, and then transferred to the freezing tube of the Beck- 

 mann apparatus. Of course every precaution was taken throughout to 

 keep absolutely clean the dishes and cloths coming in contact with the 

 extract or pulp. Freezing point determinations were made without delay 

 after the juice was extracted, to guard against any changes in it due to 

 decomposition or evaporation. 



In brief, therefore, the procedure necessary to obtain the effect of 

 lowering the concentration of the sea water consisted in lowering the 

 proportion of the sea water to fresh water by 1/28 each twenty-four 

 hours. Then at the time the water in the tubs was changed each evening, 

 four to six kelps were removed, the number depending on their size, and- 

 left over night in the same water from which they were taken; the juice 

 from these was extracted and frozen the next morning. This meant that 

 each bunch of kelps was exposed thirty-six hours to the final concentration 

 from which it was taken, but that it was exposed twenty-four hours to 

 each changed concentration preceding. This was simply to make sure that 



