53° A.H. Estahrook 



Some hay infusion was allowed to stand in a warm room until 

 it became turbid from the growth of bacteria. Part of this was 

 then filtered through a new Pasteur-Chamberlain bougie. The 

 filtrate was thus rendered free of all bacteria and was also exactly 

 the same, chemically and otherwise, as the hay infusion with the 

 bacteria in it before filtering, except for the absence of the bac- 

 teria. Halves of dividing Paramecia were put into these two 

 solutions, one with bacteria, the other without. At the end of 90 

 minutes, there was, as was to be expected, no difference in size. 

 At the age of 5 hours, the Paramecia in the hay infusion with the 

 bacterial food were shorter and thicker and measured 200.1 X 60.5 

 microns (14 specimens), while those growing in the media with- 

 out bacteria were longer and thinner; 11 of these measured 210.9 

 X 45.0 microns. At the age of 24 hours the presence of food has 

 had a marked effect. Twenty-eight specimens in the hay infusion 

 with the bacteria had increased by division to 49 specimens, 

 and these measured 193.5 ^ 62.2 microns, while the 28 specimens 

 in the medium without food had not divided at all and measured 

 205.2 X 53.4 microns. It must be said here, however, that some 

 growth of bacteria had taken place in the solution which was 

 sterile in the beginning, as it is impossible to wash Paramecia 

 absolutely free from adhering bacteria. Yet at 24 hours, there 

 was evidently an abundance of bacteria in the one medium, and 

 almost none in the other. 



Thus in the early stages of growth up to the age of about 90 

 minutes the presence or absence of food material in the medium 

 has no effect on the size of the growing animals. As we have seen 

 earlier, the greatest amount of growth takes place in the first 90 

 minutes and our experiments indicate that this increase in size 

 is due mainly to imbibition of water. From then on, the presence 

 of food in the culture fluid has an effect on the size to which the 

 Paramecia will attain. With plenty of food present the animals 

 grow shorter and thicker, and divide sooner, than those kept in 

 a medium with less food. 



It is to be noted that in the experimental work in the general 

 effects of the different chemicals studied, the question of bacte- 

 rial food does not enter in the interpretation of the results. It was 



