LITMUS MILK CULTIVATIONS 273 



hours; and subsequently at intervals of, say, twenty- 

 four hours, during the entire period they are under 

 observation, and examined 



(A) Living. 1. In hanging drop, to determine mo- 

 tility or non-motility. 



In this connection it must be remembered that 

 under certain conditions as to environment (e. g., 

 when examined in an unsuitable medium, atmosphere, 

 temperature, etc.) motile bacilli may fail to exhibit 

 activity. No organism, therefore, should be recorded 

 as non-motile from one observation only; a series of 

 observations at different ages and under varying con- 

 ditions should form the basis of an opinion as to the 

 absence of true locomotion. 



Size. In the case of non-motile or sluggishly motile 

 organisms, endeavour to measure several individuals 

 in each hanging drop by means of the eyepiece microm- 

 eter or the eikonometer (vide page 63), and average the 

 results. 



If the organism is one which forms spores, observe 



(a) Spore Formation. Prepare hanging-drop culti- 

 vations (vide page 78) from vegetative forms of the 

 organism, adding a trace of magenta solution (0.5 per 

 cent.) or other intra vitam stain (see page 77) to the 

 drop, on the point of the platinum needle, to facilitate 

 the observation of the phenomenon by rendering the 

 bacilli more distinct. 



Place the preparation on the stage of the micro- 

 scope; if necessary, using a warm stage. 



Arrange illumination, etc., and select a solitary 

 bacillus for observation, by the help of the -inch lens. 



Substitute the -j^-inch oil-immersion lens for the 

 sixth, and observe the formation of the spore; if 

 possible, measure any alteration in size which may 

 occur by means of the Ramsden micrometer. 



(b) Spore Germination. Prepare hanging-drop culti- 

 vations from old cultivations in which no living vegeta- 



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