ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 62] 



medium) and incubated for seven days at 26° C, at the end of which 

 period the liquid showed a strong- reaction for nitrates. The effect of 

 the auximones was tried on subcultures from these growths. At the end 

 of forty-eight hours all the flasks to which auximone had been added 

 shewed a thick scum on the surface of the liquid, and at the end of six 

 days were found to contain no trace of nitrate, while in the control 

 flasks, without, auximones, no scum had developed and nitrification had 

 proceeded normally. These scum organisms, which were present in the 

 original soil cultures, showed two predominant types of organisms : a 

 thin beaded form and a spindle-shaped form. It was found that the 

 presence of both these forms was necessary for scum formation, as when 

 either organism in pure culture was grown in nitrifying solution plus 

 auximone, characteristic scum never developed. The best results were 

 obtained from new loam from a virgin field, though loams, clay, and 

 gravels also gave positive results. A stock for experimental purposes can 

 be obtained by sterilizing soil, putting aside for a week, and then 

 saturating with a suspension of scum-forming organisms. The stock is 

 then allowed to dry down at room temperature under sterile conditions, 

 and stored in a bottle. This stock can be depended on to yield a good 

 growth of scum in from two to three days in the presence of auximones. 



Methyl-violet as a Means of Differentiating' the Coli-typhoid 

 Group.*— A. Botez has elaborated a new technique, based on the reduc- 

 tion of methyl-violet as a means of differentiating members of the 

 coli-typhoid group of organisms. A stock solution of methyl-violet (5b) 

 is made up to the strength of 5 parts per 100, and - 2 ccm. of this solu- 

 tion is added to each 10 ccm. tube of broth. In this medium Bacillus 

 ty/iltosus gives no change even after fifteen days, B. paratyphosus A 

 gives partial change, the colour of the medium becoming pale violet, 

 while B. jHiratyphus B and B. coli destroy the colour completely in forty- 

 eight hours ; the original colour of the broth re -appearing. Similar 

 results are obtained on agar plates if methyl-violet in the same propor- 

 tions is added to the agar before pouring the plates. The reduction of 

 methyl-violet by certain organisms, and the non-reduction by others, 

 is said to be a new distinctive characteristic, the reduction processes 

 involved being as yet uninvestigated. 



Method of Collecting- Diatoms from Surface of Mud.f—O. Kendall 

 states that the following method will be found to be of great help in 

 gathering material free from excess of sand and foreign particles, 

 especially on the shores of tide-water. The method requires that the 

 surface of the mud be uncovered by the tide. The spot for working is 

 found by the presence of a brownish coloured film, generally in streaks 

 or patches, on the sand surface. It has been found that by removing 

 the film of diatoms with a spoon large quantities of sand and mud are 

 taken up at the same time, making its removal difficult in the cleansing 

 process. 



* C.R. Soc. Biol. Paris, lxxviii. (1915) pp. 489-90. 

 t Trans. Amer. Micr. Soc, xxxiv. (1915) pp. 53-4. 



