296 GEORGE WAGNER. 



In older colonies the attractive substances seem to develop far 

 above the optimum amount. In such culture water the amount 

 can be again reduced by filtering and allowing the filtrate to 

 stand over night in an open dish. Whether such reduction is 

 by volatilization or oxidation, or by both, I do not know. Cer- 

 tain it is that to such a liquid Oxytricha taken from the same cul- 

 ture from which it came, react positively. 



Ordinarily a mount from any culture will be indifferent toward 

 its own filtered culture water, if both remain unaerated. But 

 if from a culture a highly concentrated mass of individuals are 

 taken and kept for a few hours in a small watch glass, and then 

 mounted, they will give a strong positive reaction toward a drop 

 of water from their own original culture. Evidently here a close 

 aggregation of individuals has supercharged the. water, hence a 

 positive reaction to the original culture solution of lesser strength. 



Peculiarly, of two colonies of Oxytricha each, unaerated, was 

 negative to the culture water of the other, but when aerated it 

 became positive, the introduced drop in both cases being un- 

 aerated. This again points to a marked difference between cul- 

 tures, as. several other facts do. To this phase of the subject I 

 expect to recur in another paper. 



In a search for a clue to the unknown attractive substances, I 

 tried many organic acids, sugar, urea, acetic aldehyd, potassium 

 cyanide, ammonia, and a few others, but always with purely neg- 

 ative reactions. The possibilities of the case are of course nearly 

 endless, but should opportunity offer, I would wish to experiment 

 with organic sulphur compounds, and with compounds of am- 

 monia, and this purely on the empiric basis of the odors of Oxy- 

 tricha cultures. 



Zoological Laboratory, 



University of Wisconsin, 

 January 27, 1908. 



