and Laboratory Methods. 2273 



is taken between the thumb and forefinger of the left hand, the knife is held in 

 the right. The potato is halved in the manner shown in Fig. 10. Without 

 allowing the cut surface to come in contact with any object the halves are sepa- 

 rated, each half being placed under one of the tumblers. The other potatoes 

 are treated in the same manner. The blade of the knife should be heated be- 

 fore cutttng each potato. 



If the sterilization has been successful and the subsequent halving and hand- 

 ling of the potatoes done with sufficient care, the halves of the potatoes would 

 show no subsequent change except that due to dessication. 



It is important to remember that the covers (tumblers) should not be re- 

 moved except when absolutely necessary, and then should be returned as quickly 

 as possible. 



Inoculation of the Potatoes. Remove the cover from one of the potatoes, 

 sprinkle over its surface a very few grains of dirt from an unwashed potato or from 

 the floor. Expose another to the air of the room for half an hour. Over the 

 surface of a third spread with the tip of a knife blade, which has been heated 

 and allowed to cool, a drop of milk or water. Without heating the knife rub the 

 blade over the surface of the fourth potato and again over the fifth half, leaving 

 a space '4 inch wide next to the edge of the potato which is untouched by the 

 knife. The remaining sixth piece should be left uninoculated as a control or 

 check on the work. 



These cultures are now to be placed away from the light and kept at the 

 temperature of the room or slightly above. 



Observation of Cultures. Examine these cultures daily or oftener and note any 

 changes which occur. After several days describe the color, size, and elevation 

 of areas of growth (or " colonies" as they are called). Any colonies showing 

 bright colors or other marked characters may be transferred to new culture 

 media for further study. In making the transfer a hat-pin heated red hot in a 

 flame, and allowed to cool, can be used. All possible precautions to prevent 

 contamination should be observed. W. D. Frost. 



University of Winconsin. E. G. HASTINGS. 



A simple and effective method for removing air bubbles from microscopic 

 material is suggested as follows : A small syringe, having a glass barrel, vul- 

 canite mounts, and leather packing to the piston, is the only apparatus required. 

 Select one that is as nearly as possible air tight, unscrew the top and remove 

 the piston. Close the nozzle with a small piece of beeswax, half fill the barrel 

 with distilled water, and into this drop the section or tissues to be treated. Re- 

 place the piston and screw on the top. The syringe being inverted and the plug 

 of wax removed, the air is driven out of the barrel by raising the piston till the 

 water begins to flow out of the nozzle, after which close the aperture with the 

 finger and lower the piston. A partial vacuum is thus formed, and the air 

 rapidly escapes from the cells of the tissue, collecting in the point of the 

 syringe. By removing the finger and raising the piston the liberated air is 

 forced out; this may be repeated several times as long as air is being expelled 

 from the material. The same mode of operating is applicable to objects that 

 are to be mounted in Canada balsam if oil of turpentine be used instead of 

 water, and if the objects to be mounted are quite dry before immersion in the 

 XMX^^XiVvci&.-^Knojvledge. 



