310 



ROBERT T. HANCE 



crease slowly through evaporation.^ The salt slowed the con- 

 traction rate but did not in any way influence the number of 

 vacuoles. The most marked effect in this direction was while 

 the animals were still unaccustomed to their environment. 

 After they had become somewhat acclimated, to the new con- 

 ditions after which the rate of pulsation became more normal 

 although it never regained the usual rapidity. This may account 

 in part for the varying results noted below. 



Two vacuoled animals. 



Three vacuoled animals. 



CONCEN- 

 TRATION OF 

 SALT 



per cent 



0.06 



0.1 



0.06 



0.5 



1.0 



2. The effect of cold on the rate of contraction. Cold slows the 

 rate of contraction markedly and extreme cold, i.e., 1° to 2°C. 

 apparently brings contraction almost to a complete stop. 



3. The volume of the vacuoles of the two races. In making this 

 comparison the volume of the animals was calculated in the 

 following manner. The percentage of difference in weight of a 

 paramoecium modeled in clay and a cylinder of the same length 

 and diameter made of the same material was determined. The 

 volume of a cylinder the length and diameter of a living para- 

 moecium was calculated and the volume of the paramoecium 

 was obtained by reducing the volume of the cylinder by the de- 

 termined percentage of difference between the clay models. 



1 It might be noted here that cultures containing a small percentage of salt 

 thrived wonderfully and the infusion seldom became as murky or as bad smell- 

 ing as the untreated cultures. It seems likely that the salt prevents the great 

 growth of bacteria producing putrefaction, but it seems to interfere in no way 

 with the supply of food for the paramoecia. Animals treated in this way are 

 more tough and when they burst under pressure the protoplasm oozes out in a 

 thick mass instead of the usual thin stream. Frequently the animal is able to 

 clear itself of the extruded mass and the mutilated area is covered over. Under 

 normal conditions the ejection of the protoplasm is so rapid that there is no 

 possibility of this recovery. This treatment might be of assistance with indi- 

 viduals to be operated on. 



