INFECTIONS OF THE DIGESTIVE TRACT 137 



methyl mercaptan is as follows: One hundred cubic 

 centimeters of the culture to be examined are trans- 

 ferred to a flask communicating through a calcium 

 chloride tube with an Erlenmeyer flask containing 

 isatin dissolved in concentrated sulphuric acid. A 

 current of air is then drawn through both flasks so 

 that any mercaptan given off from the culture flask 

 will enter the isatin-sulphuric-acid flask. The pres- 

 ence of mercaptan is indicated under these conditions 

 by a gradual change of the isatin solution from red to 

 olive-green or grass-green. 1 In order to save isatin 

 the reaction may be carried out substituting a test- 

 tube containing about ten cubic centimeters of the 

 isatin-sulphuric-acid mixture for the Erlenmeyer flask. 

 The method is not adapted for quantitative deter- 

 minations, but some idea can be gained through it 

 of the quantity of mercaptan present in the culture, and 

 it further serves to indicate differences in the amount 

 formed in different cultures. Twenty-five milligrams of 

 a one per cent, solution of methyl mercaptan suffice 

 gradually to alter the isatin red solution (about fifty cubic 

 centimeters) to a deep green in the course of ten minutes. 

 Reactions as strong as this are occasionally obtained 

 from one hundred cubic centimeters of a bacterial cul- 

 ture in the course of five or ten minutes. Frequently 



1 This method has been used by Niemann, ("Ueber die Abspal- 

 tung von Kohlensaure, Mercaptan und Schwefelwasserstoff beim 

 Kochen einiger animalischen und vegetabilischen Nahrungsmittel," 

 Archiv f. Hyg., xix, p. 126, 1893); also by Bauer, ("Ueber die 

 Einwirkung gespannter Wasserdampfe auf Keratin," Zeitschr. f. 

 physiol. Chem., xxxv, p. 346, 1902). 



