80 ISOLATION OF AEROBIC MICRO-ORGANISMS 



and covered by a bell jar (fig. 71). The table rests on screws which enable it to be 

 levelled with the aid of a small spirit level. Two lateral tubes fitted to the box 

 allow a stream of cold water (or if agar is being used, warm water) to be passed 

 through it, and ice can also be put into the box if necessary through a large opening 

 in the bottom closed with a screw cap. 



5. Three tubes of melted gelatin and three Pasteur pipettes. 



Technique. 1. Pour a little perchloride of mercury solution into the large glass 

 dish, and by rotating the dish wash every part of its interior with the antiseptic. 



Lay two or three thicknesses of filter paper in the bottom of the dish and saturate 



FIG. 71. Cooling stand for plate cultures. 



them with perchloride solution. (This constitutes a moist chamber, the object being 

 to prevent the gelatin plates drying up.) 



Wash the glass stands (fig. 70) with perchloride, and place one of them in the 

 bottom of the dish. 



2. Place the cooling stand on the operator's left, level it and fill it with cold or 

 iced water. Wipe the top carefully to remove any dust that may be on it, and 

 wash the inside of the glass cover with perchloride solution. 



3. Sowthe three tubes of gelatin, 1,2, and 3, as in the gelatin plate method (p. 78 A (i)). 



4. Take one of the glass plates, tear off the paper cover along one of the edges, 

 hold it by one of its corners between the thumb and first finger of the right hand 

 [or better in a pair of sterile forceps], slightly raise the glass cover with the left 



hand, and lay the plate on the glass support 

 already placed there. Replace the glass cover. 



5. Take the plug out of tube 3, flame the upper 

 2 or 3 cm. of the tube, and then while not raising 

 the glass cover more than is necessary introduce 

 the mouth of the tube beneath it, pour the gelatin 

 on to the centre of the glass plate and spread it 

 with the upper flamed part of the tube. With- 

 draw the tube, replace the bell jar, and allow 

 the gelatin to set. 



6. When the gelatin has set, raise the bell jar 

 again, take hold of the glass plate by one of its 

 corners, transfer it as quickly as possible to the 

 moist chamber (the cover of which is raised with 



the left hand, after replacing the bell jar), and lay it on the glass stand. 



Bridge the glass plate with the second glass stand, and replace the cover of the 

 moist chamber. 



It will be noticed that the gelatin has not come in contact either with the walls 



FIG. 72. Arrangement of the glass 

 plates in a moist chamber. 



