Isolation of the Singh Bacterial Cell. 



223 



The slip is then placed on another moist cell, incubated for 

 twenty-four hours, and examined for growth under the microscope. 

 When a solid medium is employed, if the original observation was 

 correct, one colony only will have developed. 



If the micro-drop really contained more than one micro- 

 organism, separate compact little colonies can be seen after twenty- 

 four hours, corresponding in number with the organisms originally 

 present. 



The same is true of many organisms, such as streptococci, even 

 when incubated in hanging drops of liquid medium. 



J c 



j[2=^ 



i-i^ 



A.I Hanging-drop slide with filter-paper ring iu position, 

 shown in plan, and iu B longitudinal section. C. Filter- 

 paper ring. D. Micro-drop on cover-slip. E. Drop 

 culture after incubation with single colony. 



In this way the accuracy of the original observations is 

 controlled. 



A portion of the growth thus obtained from a single cell is 

 removed on an ordinary loop and transferred to a suitable medium 

 for more massive growth. With ordinary care the risk of con- 

 tamination is negligible, a point wdiich has been established on a 

 long series of observations. 



In working with delicate organisms the process miist be carried 

 out at body temperature on a warm stage. In this case the centre 

 of the cover-slip is the coldest part of the moist cell, and to avoid 

 steaming and a rapid flooding of the micro-drop, the filter paper 

 ring must be replaced by a small drop of saline only two or three 

 times as large as the micro-drop. 



When the observation is complete, the large drop of medium is 



