ESSENTIALS OF BACTERIOLOGY 



long axis with a knife that has been passed through the flame. 

 The two halves are kept in contact until they are lowered into 

 the moist chamber, when they, of their own weight, fall aside, 

 the cut surface uppermost. They are then ready for inocula- 

 tion. 



Esmarch's Cubes. The potato is first well cleaned and 

 peeled. It is then cut in cubes \ inch in size. 



These are placed, each in a little glass dish or tray, and then 

 in steam-chest for one-half hour, after which they are ready 

 for inoculation (the dishes first having been sterilized in hot-air 

 oven) . 



Test-tube Potatoes. Cones are cut out of the peeled 

 potato and placed in test-tubes, which can then be plugged 

 and easily preserved. 



Roux's test-tube (Fig. 21), specially designed 

 for potato cultures, consists of a tube with a 

 small constricted portion at the bottom, in which 

 water may be kept to keep the potato moist. 



Manner of Inoculation. With a platinum 

 rod or a spatula (sterilized) the material is spread 

 upon one of the slices, keeping free of the 

 edges. The growth on this first, or original, 

 potato will be quite luxuriant, and the individual 

 colonies often difficult to recognize; therefore 

 dilutions are made (Fig. 22). 



From the original or first slice a small portion, 

 including some of the meat of the potato, is 

 spread upon the surface of a second slice, 

 which is first dilution. From this likewise a 

 small bit is taken and spread on a third slice, or 

 second 'dilution, and here usually the colonies 

 will be sparsely enough settled to study them in their indi- 

 viduality. 



This is the principle carried on in all the cultivations. It 

 is a physical analysis. 



Potato and Bread Mash. These pastes are used chiefly in 

 the culture of molds and yeasts. Peeled potatoes are mashed 



Fig. 21. Tube 

 for potato cul- 

 ture. 



