ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



303 



of Drigalski and Conradi, MacGonkey and Endo, and the outstanding con- 

 clnsion derived from these researches was that all these media eliminate 

 a very large proportion of typhoid (and even paratyphoid bacilli), and 

 do not to any very notable degree inhibit the growth of B. coli. The 

 following table shows the kind of results that were obtained : — 



The good result here shown with Endo's medium was only obtained 

 when the medium was very fresh. The colonies of B. coli on Endo's 

 medium are well developed, of a deep red colour, and gradually acquire 

 an intense metallic sheen, while those of B. typhosus are at first only 

 faintly rosy in colour, and though they eventually become red they 

 never acquire any metallic lustre. 



It is suggested that this medium might well be used instead of 

 MacConkey's medium in the technique of the brilliant green enhance- 

 ment method of Browning, Gilmour and Mackie. 



The authors have devised a technique for the rapid isolation of 

 B. typhosus or B. paratyphosus A. or B. in twelve or twenty-four hours 

 by means of a single plate. The method consists of the subjection of 

 an ordinary agar plate, liberally spread with the bacterial emulsion, to a 

 graduated exposure to the rays of an arc light, silver electrodes giving 

 the best results. 



The lamp consists of two small metal pillars bracketed on an insu- 

 lating slate base. The pillars carry the horizontal arms upon which 

 electrodes, water-cooled after the manner devised by Bang, are screwed. 

 These arms can be approximated to each other by means of thumb- 

 screws. They consist of an outer tnbe within which runs a smaller 

 inner tube, serving as inflow for the cooling water, which returns by the 

 outer tube. The arc is made by an electric current of 5 to 7 amperes, with 

 a voltage of 30 to 35 volts. In exposing an inoculated plate, the lid is 

 removed and the agar surface is directly exposed to the arc at a distance 

 of about 6 cm. Upon the Perti dish is placed a sheet of blackened 

 metal in which an oblong window has been cut. By means of another 

 sheet of blackened metal, the window, at first fully opened, is gradually 

 closed, the different exposures along the strip varying from 30 to 240 

 seconds. In making a plate, from 0*5 to 1 c.cm. of faeces are broken 

 down in 2*5 c.cm. broth and allowed to stand for about two hours. 

 Two or three drops are then taken from the upper part of the fluid and 



Y 2 



