452 PROCEEDINGS OF THE AMERICAN ACADEMY. 



in its proportions. The effect of this upon the animals has been par- 

 tially overcome by doubling or even trebling the concentration of the 

 above formula so that, if added to distilled water, it would have repre- 

 sented 200 to 300 molecular parts in 100,000. The excess of constituents 

 known to be favorable was relied upon to nullify, in part at least, the dis- 

 turbance of balance clue to the addition of food. The same observation 

 applies to the use of tap-water, which was customary for mass cultures. 



Having added to about 3500 cc. of tap-water, contained in a 4000 cc. 

 jar, sufficient of the above salts to make the required concentration when 

 the jar is full, the next step was the addition of some dry leaves or dead 

 reeds or both. The smaller the amount the more quickly will the cul- 

 ture develop, but when the supply is too scanty the culture cannot be- 

 come long-lived. Sometimes it is desirable to heat the leaves and reeds 

 to boiling and then to add the cooled mixture to the salt solution. This 

 causes the solid material to sink immediately, thus facilitating observa- 

 tion at the upper part of the jar, and it also hastens the chemical changes 

 that must precede the rapid growth of Stentor. The final step is to 

 "seed" this culture with a mixture of all sorts of Infusoria and other 

 living material from thriving cultures, including, of course, a large pro- 

 portion of Stentor. If good cultures are on hand, it is advisable to stir 

 up one of them and transfer about 500 cc. of its liquid to the new cul- 

 ture. If the new culture was successful, it showed the previously de- 

 scribed localized growth of Stentors at some time within a week after it 

 had been started. Among the various foods tried was a decoction of 

 barley made by boiling a few grams for about one-half hour. The liquid, 

 containing many particles in suspension, was poured off from the barley 

 grains. When this was very largely diluted with tap-water and seeded, 

 many Infusoria, especially Vorticellae, grew well, but no abundant cul- 

 ture of Stentor could be so raised. The results were somewhat better 

 when the extract of barley was added to the salt medium mentioned above. 

 Tests made independently of the cultures showed that the Stentors did 

 not use as food the particles obtained by boiling the grain. But no other 

 medium equalled this extract in the rapidity of the divisions at first 

 produced. The Stentors became smaller without subsequent growth. 

 Evidently the effect produced was stimulation, not feeding. 



The medium probably had a favorable salt constitution, derived from 

 the grain, and it had comparatively little power of fermentation. The 

 classical hay infusion was also tried. While Paramaecia and many 

 other Infusoria grew abundantly in cultures set with hay, Stentor uni- 

 formly failed to produce successful cultures. When a hay infusion 



