TEXT-BOOK OF BACTERIOLOGY. 79 



in the direction of their length, being- held by the finger and thumb 

 of the left hand, finger and thumb to be previously dipped in \% 

 corrosive sublimate solution. 



Next, with a sterilized scalpel or a platinum loop take the mat- 

 ter to be inoculated, and by spreading and rubbing 1 extend it as 

 evenly as possible over the surface of the slice. It is well to have 

 a border or margin of about one cm. around the edge; the culture 

 will afterward show a clearly-limited, definite growth, upon which 

 is best calculated to form a sound judgment. Foreign growths, 

 too, proceeding from germs that have by some chance escaped de- 

 struction (if such there be) are generally found to start from the 

 edges, so that it is desirable to avoid contact with them. When 

 the slice is properly inoculated it must be kept from drying- up and 

 from pollutions from the air. A number of such slices are, there- 

 fore, placed in large glass dishes, with a layer of damp filter paper 

 at the bottom, the lid only being removed in case of necessity. 



This " moist chamber " must not be fairly wet, for in that case 

 drops of water are apt to form on the inside of the lid and fall down 

 on the slices, disturbing the quiet development of the culture. 



It is unnecessary and even dangerous to use sublimate for the 

 cleaning of the dishes or the moistening of the blotting-paper. The 

 inoculated surface of the potatoes does not come into contact with 

 anything- dangerous to it, and the sublimate solution, if it gets to 

 the slices, can only do harm and render the culture useless. 



There is another process of preparing- potatoes for bacterium 

 culture, very much simpler and for many purposes equally suffi- 

 cient that of E. von Esmarch. 



Sterilize a number of small double glass dishes (such as are often 

 used for holding staining fluids) in the hot-air oven. Some pota- 

 toes are peeled with an ordinary kitchen knife and washed clean 

 under the faucet. Then carefully cut out the eyes and the " bad 

 places," and cut the potatoes into slices about 1 cm. thick, placing 

 one such slice in each of the dishes. These dishes, with the potato 

 slices, are then exposed for about one and one-half hours to the 

 action of the steam generator, in which they are well boiled and 

 sterilized. The skin, as the protector against foreign g-erms, being- 

 here removed, the dang-er of after-pollution is far less, and as the 

 evaporation proceeds very slowly in such small dishes, the danger 

 of the slices drying- up is small. General use can, therefore, be 

 made of the surface; it can be inoculated and the developed culture 

 kept for months. Krai in particular has made this fact subser- 

 vient to his purposes in the preparation of his magnificent cultures 

 for demonstrations. 



