46 KANSAS UNIVERSITY SCIENCE BULLETIN. 



When the cultures have grown, cells may be removed by- 

 means of the same apparatus to a new cover or test-tube ; or, 

 if there is room, they may be reselected on the same cover. 

 I have experienced little difficulty from contamination. For 

 many months I have carried on experiments with yeasts and 

 bacteria at the same time, and contamination of the one by 

 the other has been almost unknown, and drops not inoculated 

 uniformly remain sterile. So it seems improbable that yeasts 

 are ever contaminated with other yeasts, or bacteria with 

 bacteria. Even if one could not observe the origin of the 

 yeast and B. coZ* variations, for instance, and follow their first 

 development after isolation, one could hardly attribute the 

 origin of these new races to contamination, considering the 

 small chance that an organism should enter which has so 

 many characteristics in common with the parent culture. 



I have described above the later and more elaborate appa- 

 ratus for isolating micro-organisms. In routine work, unless 

 an objective of higher power than a one-sixth is to be used, I 

 often employ the simpler method first devised. The pipette 

 holder is here dispensed with, and the position of the glass 

 box reversed so that its open end is toward the right. The 

 right hand, steadied by the stage, holds the pipette, and the 

 fine adjustment of the microscope and the mechanical stage 

 are operated by the thumb and second finger of the left. 

 This method has the advantage of simplicity and speed, es- 

 pecially in the matter of changing pipettes ; but requires 

 some steadiness of hand and considerable practice in manipu- 

 lation ; for the operation once begun, one cannot lose sight 

 of the tip of the pipette without risking contamination. I 

 find little difficulty, however, in working under the one-fourth 

 and one-sixth objectives with one-inch ocular by this free- 

 hand method. 



Besides the work of isolating variations, I have frequently 

 used the above methods as a substitute for plate cultures in 

 isolating organisms. I have successfully isolated single 

 spores of fungi, single cells of algae, various yeasts, and many 

 bacteria, including Streptococcus, from pus. I have found 

 little difficulty in obtaining colonies of amoebae or infusoria 

 grown from single individuals. The method has some ad- 



