NUTRIENT MEDIA. 



51 



FIG. 22. 



from the steam-oven and holding it between his thumb and 

 index finger in the short axis, he divides the potato in its 

 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 inoculation. 



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 hour, after which they are ready for inocu- 

 lation (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. 22), 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. 23.) 



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 

 viduality. 



This is the principle carried on in all the cultivations, 

 a physical analysis. 



Potato and Bread Mash. These pastes are used chiefly in the 

 culture of moulds and yeasts. Peeled potatoes are mashed with 

 distilled water until thick, and then sterilized in flasks | of an 

 hour for three successive days. 



Tube for potato 

 culture. 



their indi- 



It is 



