536 THE MEASUREMENT OF BACTERIA. 



A large diagram of types may be employed, but perhaps a 



better idea is obtained when the types are reduced to sizes 



approximating those observed with the 



^^^ ^N» ^»^Vv oil-immersion. These are given in the 



03 023 0-2 accompanying figure (fig. 3), where the 



/ \"\ "syS *."• : * long rods measure three millimetres 



...,, ~~, ", * and the shorter rods 1*2 mm. 



The diameters of micrococci, strepto- 

 thrix and other forms might be con- 

 firmed after micrometer measurement 

 by comparing the coccus, etc., relative 

 to the micrometric scale division lines, with lines ruled at 

 intervals of 1/2 mm. (the length of the smaller diagrammatic 

 organisms) upon a coverglass which is superposed over the 

 shorter diameter of the diagrammatic types. If the coccus 

 or streptothrix occupies a space in the divisions of the eye- 

 piece similar to that occupied by one of the types when viewed 

 under such a ruled coverglass, it is obvious that the diameter of 

 the coccus, etc., will be the type number multiplied by the value 

 of the micrometer divisions. Such rulings can be made upon a 

 coverglass by dipping the latter into a dilute solution of gelatine 

 (0'5 %) and ruling the lines with Indian ink upon the thin dry 

 gelatine film. 



[Printed off November -20th, 1900.] 



