171 



0.3o/o NaCI, 0.2o/o secondary potassium phosphate and 0.1 o/ magne- 

 sium sulphate with its water of crystallisation, were taken. (The 

 last two salts can he dispensed with without danger; Cole & Onslow 

 do not mention them). To favour the growth of Pfeiffer's hacillus 

 the air coccus was previously grown on the medium for 2 days; 

 1 — lV2°/oo dissolved sheep blood corpuscles were added after which 

 the mixture was filtered through a Berkefeld filter. 



In series VIII (Oct. 1920) cultures in haemoglobin broth with 

 a little gelatine were used. (Before inoculation the medium had 

 been heated to about 70°, which coagulated the haemoglobin). After 

 the cultures had been in the incubator a week for the gelatine 

 liquefaction lest, which as previously stated, was always negative, 

 the indol test was done on them. In a number of cases this was 

 carried out by pouring a mixture of 2 parts of the paradimethyl- 

 amido-benzaldehyde reagent and 1 part of the potassium persulphate 

 solution, on the solidified gelatine medium. A positive reaction con- 

 sisted in the development of a red ring at the boundary between 

 the medium and the reagent. The remainder of the cultures were 

 melted at 37° and then mixed with the two liquids in the usual 

 manner. The reaction was very distinct with both methods of 

 carrying out the test. 



Experiments IX— XII which were performed in Aug. 1920, but 

 for typographical reasons are placed last, constitute a connected 

 investigation designed with the object of finding out the effect on 

 the formation of indol, of varying the substances from which it is 

 formed. 



In series IX Bacillus coli-fermented broth with the addition 

 of lo/o ereplon (,,vollstandig abgebautes Fleischeiweiss nach Prof. 

 Dr. Abderhalden" from Meister, Lucius, and Bruning) was used 

 instead of peptone. In X the same casein medium as in VII was 

 employed. In XI a watery solution of lo/ peptone Chapotaut 

 + the same salts as in the casein medium, was used. In XII 

 Bacillus coli-fermented broth with Witte peptone was used. All 

 the media were sterilised in the steam steriliser. They were inocu- 

 lated with the air coccus. After 2 days' incubation at 37°, 2°/ 0C , 

 dissolved sheep blood corpuscles were added, and then the media 

 were filtered through a Berkefeld filter. 



In series VII and IX— XII 4 days was allowed for incuba- 

 tion. To obtain a numerical expression for the strength of the 

 reaction, a fuchsin solution was added to a series of tubes, 1, 2, 3, 

 etc. containing boiled bacterial culture in such quantities that tube 

 No. n contained fuchsin in a concentration 2"— • X 10- 6 . Tube 

 No. 1 assumed a light rose colour; No. 7 became dark red. The 

 strength of the indol reaction was then given by the number of 

 the fuchsin tube the colour of which most closely matched the 

 colour of the reaction tube, in intensity. 



In series Vila the positive reactions, which are only designa- 



