378 



xviii.— a key for the identification of 



bactp:ria. 



By Joseph Kitchin, F.R.M.S. 



In working on the culture and identification of bacteria in 190G, 

 the writer found great difficulty in comparing the characters of a 

 large number of organisms, and to assist in comparing and 

 differentiating them he then devised a system of index numbers 

 which is covered by the table given on page 379. 



A numerical index for comparing the morphological and 

 physiological characters of organisms used by the Society of 

 American Bacteriologists is described by Mr. J. Percival in 

 " Agricultural Bacteriology," p. 60, and a modification of the 

 system was put forward by Mr. John Golding in the " Journal of 

 the Board of Agriculture," March 1912, pp. 1001-4 (noticed also 

 in the " Journal of the Royal Microscopical Society," of August 

 1912). It is suggested that the index described in this note is 

 simpler and easily memorized, so that characters can be read at 

 sight without need of reference to the index table. 



The idea is to form an index number for the microbe examined, 

 consisting of eleven digits, of which the first two (which may con- 

 sist of any of the numbers from 1 to 9) indicate respectively the 

 kind of microbe and the colour of the colony. The remaining nine 

 digits, divided by commas into sets of three (as in ordinary 

 numbers), give the characters of the microbe, and as only one of 

 the numbers 1 to 9 occupies each space, one knows at sight (after 

 memorizing the index) what character is indicated by each num- 

 ber, and if the number is represented by one sees at once, by 

 reference to the numbers to left or right, what character it is that 

 is absent. 



The index need not be a rigid one, and the number of digits 

 can be increased or decreased, and different characters can be 

 assigned to the various positions. It may be useful both in 

 medical, botanical and industrial bacteriology. 



