376 



SCI±JNCE. 



[N. S. Vol. XV. No. 375. 



ing the operation until the desired thick- 

 ness is reached. As soon as the collodion 

 has set, the tube may be repeatedly im- 

 mersed in water at about 25 °C. to hasten 

 the drying of the sack. When this is ac- 

 complished pour distilled water into the 

 open end of the tube, and applying the 

 mouth, force the Avater, which carries the 

 collodion ahead of it, through the perfora- 

 tion in the tube. The water now creeps in 

 between the sack and the tube and this 

 process is aided and made to progress even- 

 ly on all sides by slightly twisting back 

 and forth, on the free end of the sack. 

 Allien the water has traversed the entire 

 length of the sack, the latter slips off eas- 

 ily into the hand. The water, by its 

 pressure, not only releases the sack, but 

 tests it for weak places or perforations at 

 the same time. Tubes may be made from 

 one sixteenth inch to two inches in diam- 

 eter and twenty inches long. 200 c.c. of 

 saturated magnesium sulphate were dial- 

 yzed out through such a sack against run- 

 ning water in four hours and twenty 

 minutes. Parchment requires seven to 

 eight days to accomplish the same. 



Neutral Red in the Examination of Water: 

 Eenest B. Irons, University of Chicago. 

 In 1898 Rothberger found that B. coli 

 communis will reduce neutral red in a cul- 

 ture medium, changing the color from red 

 to a canary yellow, with an accompanying 

 green fluorescence. Schleffler . tested a 

 number of races of B. coli and found that 

 all gave the neutral red reaction. In 1901 

 Savage employed neutral red for the de- 

 tection of B. coli commiunis in water. He 

 concluded that a positive reaction, ob- 

 tained with neutral red, while not certainly 

 diagnostic of B. coli, yet in the vast ma- 

 .iority of cases, points to the presence of 

 that organism, and that in the ease of the 

 fifty waters examined, the margin of error 

 in assuming that B. coli was present where 



a positive neutral red reaction was ob- 

 tained, was less than five per cent. 



The object of the present experiments 

 was to determine further the value of neu- 

 tral red in the routine examination of 

 water. Following the suggestion of Sav- 

 age, ordinary bouillon was used, to which 

 was added one-half per cent, of dextrose 

 and one per cent, of a one-half^ per cent, 

 aqueous solution of neutral red. All cul- 

 tures were kept at 37° C. Determinations 

 were made by the dextrose fermentation 

 tube and neutral red methods in exact 

 parallel. Samples of forty-five waters were 

 employed with a number of dilutions of 

 each, such that in the case of each water 

 B. coli was almost always found in the low- 

 est, and rarely in the highest dilution. In 

 this series 285 determinations were made 

 by either method, mth thirty-five per cent, 

 positive results for the fermentation tubes 

 and forty-seven per cent, positive with 

 neutral red. Of the neutral red tubes 

 showing positive results when the corre- 

 sponding fermentation tubes were nega- 

 tive, 31 were examined for B. coli. From 

 five of the 31 typical B. coli were isolated, 

 and from 25 organisms were isolated which 

 differed more or less from B. coli, but 

 which gave the neutral red reaction. Of 

 these 25, 18 gave no gas in dextrose 

 bouillon. In all, 122 cultures were exam- 

 ined. Of 17 conforming culturally 

 to B. coli, 15 gave a positive and two 

 only a very slight reaction with neutral 

 red. Of eleven gas-producing organisms, 

 differing slightly from B. coli, four gave 

 positive and seven negative reactions. 

 Pour organisms conforming culturally to 

 B. cloacce gave complete reactions. Of 

 65 non-gas-producers three gave decided, 

 and 24 partial, reactions with neutral 

 red. 



The results show that the neutral red 

 reaction is produced, under the conditions 

 of the test, by a number of water bacteria, 



