6-i Scientific Proceedings, Royal Dublin Society. 



that B. violacens produces spores, the cultural characteristics of this organism, 

 owing to their variation, agree with his description of both B. violaceus and 

 B. ianthinus. 



In order to test the effect of media on colour-production, an inorganic 

 food-basis solution was made up as follows : — 



0-5 grm. NaCl. 

 1-0 grm. KH^POi. 

 0'5 grm. MgS04. 

 Trace of CaOU. 

 O'OOS MgCOa. 



Distilled water to 1 litre. 



This solution was divided into five parts, to each of which was added 

 1'5 per cent, of agar-agar as follows : — 



No. 1. Inorganic food-basis with agar. 



,, 2. Same as No. 1, witli two per cent, lactose. 



,, 3. „ ,, ,, two per cent, starch. 



,, 4. „ ,, „ two per cent. urea. 



,, 6. ,, ,, ,, two per cent, peptone. 



Slope cultures of the bacillus were made on all these media and incubated 

 at 20° 0. Slight growth occurred ou Nos. 1 and 4 ; better growth on 

 Nos. 2 and 3 ; and good growth and colour were found ou No. 5 (the 

 peptone) in about five or six days. 



Cultures were made in a 0'29 per cent, potassium nitrate solution free 

 from nitrites ; and after five days' incubation the medium was found to 

 contain nitrites, showing the reduction of nitrates by the bacillus. 



Preparation and Separation of the Pigment. 



Slices of potato were sterilized in Petri dishes, and inoculated by quickly 

 pouring over them an emulsion of bacteria. This emulsion was obtained by 

 pouring about 10 c.c. of sterile water into a well-coloured culture of the 

 bacillus on an agar slope. After four or five days' incubation at 20°, the 

 potatoes appeared to be covered with a violet dew or " shagreenliiie " growth ; 

 and on the eighth, ninth, or tenth day the growth appeared more blue and 

 slimy, the slime being due in part to the partial decomposition of the potato. 

 The growth was then lightly scraped oS the potato with a spatula and placed 

 in a " Sohxlet thimble." The colour was extracted by distilling absolute 

 alcohol on to the growth until no more colour came over with the alcohol in 

 the siphon tube. The solution was then placed in a boiling tube and allowed 



