476 PROCEEDINGS OF THE AMERICAN ACADEMY. 



(k=1X 10~ 6 , or 1— X 10 -6 ) was very nearly as pure as one can produce 

 when working in contact with air. This statement assumes of course that 

 the containing vessel in which the experiment is performed is not a 

 source of contamination. Wherever this possibility was a factor of 

 importance I have taken pains to prove the absence of contamination by 

 the objective method of a conductivity determination. In some cases, 

 depending on the end in view, it suffices to know the degree of contami- 

 nation or its rate, or the fact that the contamination is so small in a given 

 time as to defy detection by even so delicate a method as that here used. 

 What, then, are the phenomena of the reaction of Stentor to pure 

 water ? I will first describe this experiment as it presents itself to sim- 

 ple direct observation. The distilled water used, if freshly prepared, 

 should be aerated by repeated pouring from one vessel into another in a 

 thin stream of some height. I applied both the ordinary distilled water 

 which I was in the habit of using and such as had a conductivity of 

 K — 1— X 10~ 6 . Great care is necessary to avoid the introduction of 

 contamination with the organisms, as it is of course impossible to handle 

 them except as they are contained in liquid. The method of multiple 

 transference, described on pp. 445-446, meets the requirements and 

 permits an objective (conductivity) test of its efficiency in any given case. 

 Quadruple transfers were made in this test. The solubility of the glass 

 used proved upon examination to be a negligible quantity in this experi- 

 ment. The animals show at first no noticeable signs of discomfort. If 

 undisturbed they gradually come to rest in an expanded condition, as 

 they do in any harmless medium. But after about one and a half to two 

 hours in the water of k — 7 X 10 -6 , or after about three fourths of an 

 hour to an hour in the water of k — 1— X 10~ 6 , the first evidence of 

 disintegration appears in the form of irregularities of the surface. The 

 margin of the optical section of the Stentor looks rougheued instead of 

 smooth, as it normally is. Within a short time afterwards there remains 

 only a mass of disintegrating material. The two samples of water yield 

 the same qualitative phenomena, but the onset of disintegration occurs 

 sooner in the pure water. The length of time that the animals resist 

 pure water depends of course upon their physiological condition and is 

 therefore variable. A sample of water causing disintegration within a 

 few minutes (complete destruction within fifteen minutes, as I once ob- 

 served) justifies the suspicion of its containing solid or gaseous impurities 

 that are foreign to properly distilled water. Experience with personally 

 prepared and tested waters will amply prove this statement. The treat- 

 ment of Stentor with more or less pure distilled water was frequently 



