QUALITATIVE BACTERIOLOGICAL ANALYSIS. 207 



alkali, but they are comparatively rare and, when sub-cultured, 

 are easily distinguished from the typhoid bacillus. By adopting 

 the alkaline glucose-litmus-agar the labour of investigating 

 plates is much diminished, with a little practice a large number 

 of plates can be examined in a very short time ; as a rule, only 

 about half a dozen colonies in each plate require to be fished. 

 Remy has lately suggested a modification of the potato- 

 gelatine medium. The new gelatine has a chemical composition 

 almost identical with the chemical analysis of potato ; it consists 

 of: 



Distilled water , . . . . . 1,000 grammes 



Asparagine . . . , . . . 6 - 00 



Oxalic acid . . ' . 0'50 



Lactic acid . . . . . . .- O'lo 



Citric acid ... . 0-15 



Di-sodic phosphate 5 '00 



Magnesium sulphate . . . . . 2'50 



Potassium sulphate . . . . .1-25 



Sodium chloride 2'00 



After sterilisation the gelatine is acidified with semi-normal 

 H 9 SO 4 , so that 10 c.c. of the medium shall have an acidity 

 which is exactly neutralised with 0'2 c.c. of a semi-normal solu- 

 tion of soda. Just before use, 1 c.c. of a 35 per cent, solution of 

 lactose and O'l of a 2'5 per cent, solution of carbolic acid are 

 added to each tube. In this gelatine the deep colonies of B. coli 

 are round, oval, or sometimes fusiform, and of a brownish-yellow 

 colour, fine bubbles of gas arising from the decomposition of 

 the lactose sometimes accompany the colonies. The superficial 

 colonies of B. coli are of two kinds : the first are globular, of a 

 brownish-yellow colour, and sometimes show vertical prolonga- 

 tions which are raised above the surface of the gelatine ; the 

 second are opaque films (spread out) with an irregular margin. 

 At firsh they are sometimes transparent and of a bluish colour,, 

 but later they rapidly become opaque. The colonies of B. 

 typhosus which appear at the end of two days are deep and 

 superficial. The deep colonies are bluish-white in colour and 

 much smaller than those of B. coli ; they are, however, very 

 distinct to the naked eye. The deep typhoid colonies are 

 never surrounded by bubbles of gas. The superficial colonies 

 are not generally visible until the third day. At first thev 



