ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 565 



B. Technic[ue.* 

 (1) Collecting' Objects, including Culture Trocesses. 



Method of demonstrating Bacillus coli in Polluted Water.f— To 

 100 c.cm. of double strength nutrient la'oth (+10 Eyre) there is added 

 1 crrm. of salicylate of soda ; the broth is then put into tubes (varying 

 in size) from 25 c.cm. to 1 c.cm. in each tube, and all the tul)es are 

 sterilized in the usual way and allowed to cool ; to each tul)e is then 

 added a quantity of the suspected water equal in volume to the broth 

 contained in it, and the tubes (which now contain salicylate of soda 

 equivalent to • 5 p.c.) are incubated for a period (24 to 48 hours) at a 

 temperature of 42° C. If turbidity of the broth results, Bacillus coli 

 may be suspected, and its identity will have to be proved by micro- 

 scopical examination and by bio-chemical (e.g. sugar fermentation) tests. 

 The only bacillus which is likely to grow along with coli is subtilis, and 

 they can be separated from each other, if necessary, by '• plating." If 

 incubation of the tubes be carried out at a lower temperature (87° C), 

 which the writer, G. C. Purvis, does not recommend, then B. jn-oteus is 

 also likely to grow far more vigorously than either subtilis or coli. 



B. ti/j)hosu8 (laboratory cultures) is completely inhibited by 0' 25 p.c. 

 of sodium salicylate and even by • 2 p.c, and does not grow particularly 

 well even in a O'l p.c. salicylate medium. As B. coli is considered the 

 " indicator " of sewage contamination, its detection is of importance in 

 the examination of suspected waters. 



Method of Procuring Moulds and ToruIaB from the Air Uncon- 

 taminated by Bacterial Growths.^ — This method, devised by G. C. 

 Purvis, consists in adding salicylate of soda (in 1 p.c. strength) to the 

 nutrient medium — e.g. agar, and ' plating " in the usual way in Petri 

 dishes, then exposing the plates (after the medium has set) to the air for 

 such time as may be deemed necessary. Suppose 100 c.cm. of ordinary 

 nutrient agar be taken ; this will require 1 grm. of salicylate of soda, 

 which will give 20 tubes for plating, each tube containing 5 c.cm., or 

 14 tubes each containing 7 c.cm. and a little to spare. It will be found 

 on exposing the plates — or a single plate — to the air and incubating at 

 37° C. that no bacterial colonies will have appeared, but only moulds 

 and torulse. If nutrient gelatin be used for " plating," then of course 

 the incubation will have to be carried out at a lower temperature (22" C.) 

 which is a better temperature for moulds, but gelatin is unsuitable as a 

 medium in the tropics, or even in sub-tropical climates. 



Isolation of SpirochaBt8.§ — This method is described by G. Proca, 

 P. Danila, and A. Stroe. A mixed culture rich in spirochsetes is in- 



* This subdivision contains (1) Collecting Objects, including Culture Pro- 

 cesses ; (2) Preparing Objects ; (3) Cutting, including Embedding and Microtomes ; 

 (4) Staining and Injecting ; (5) Mounting, including slides, preservation fluids, etc. ; 

 (6) Miscellaneous. 



t Lancet. 1912, ii. p. 439. 



X Lancet, 1912, ii. p. 438. 



§ C.R. Soc. Biol. Paris, Ixxiii. (1912) pp. 285-6. 



