Effect of Chemicals on Groivth 529 



Effect of Food on Growing Paramecta 



At almost every step in these experiments, the question arose 

 as to what part the presence or absence of food plays in the growth 

 of Paramecium. We have seen that during the first 90 minutes, 

 growth took place very fast. To what is this rapid growth due? 

 Is it due to ingested matter or to imbibition of water.? Growing 

 Paramecia were put into hay infusion containing India ink, and 

 it was found that no particles of the India ink were ingested into 

 the body of the animal until about 30 minutes after fission. Thus 

 the marked increase in size which takes place in the first 30 min- 

 utes in a growing Paramecium cannot be due to ingested matter 

 of any sort. The only other explanation for the increase in size 

 is the imbibition of water. 



To determine directly the efi-'ect of food upon growth in the 

 early stages, the growth of Paramecium in tap water containing 

 rather httle bacterial food was compared with the growth in fresh 

 hay infusion. Halves of divided specimens were put into hay 

 infusion, the other halves of the same specimens into tap water 

 which had been boiled and then aerated. At the end of one hour, 

 35 specimens in the hay infusion measured 1 73.1 X 40.9 microns, 

 35 in the tap water 171. 4 X 40.6 microns. We find that the 

 same amount of growth has taken place in both. 



The growth in tap water as prepared above was then compared 

 with that hay infusion in which there was dense bacterial growth. 

 Specimens just after fission were used and kept in the different 

 culture fluids one hour. At the end of that time, the Paramecia 

 in the ha\ infusion with plenty of bacterial food present measured 

 169.8 X 42.0 microns (10 specimens), while those in the tap water 

 with practically no bacterial food grew to about the same size, 

 1 71.3 X 42.3. From this experiment and the experiment before, 

 growth to the age of 60 minutes would seem to be'independent of 

 the amount of food present, as the same amount of growth takes 

 place in the tap water with no food present as in the hay infusion 

 with the large amount of bacteria. 



To see what effect food will have upon growing Paramecia for 

 longer periods of time the following experiment was performed: 



