DIPHTHERIA 43 



purposes ; this medium serves well for the cultivation of a great 

 many organisms, some of which are almost always present in the 

 mouth, so that cultures made upon it are usually very impure. 

 We use a medium which permits the development of the diphtheria 

 bacillus, and inhibits that of most other organisms. The best is 

 solidified blood-serum. 



The method in which the medium is inoculated is as follows : 

 The tube of culture medium, and the tube containing the swab, 

 are held side by side between the index and middle fingers of the 

 left hand, the mouths of the tubes pointing to the right and 

 slightly downwards. The plug of the culture-tube is then singed, 

 removed by means of a pair of forceps, and placed between the 

 ring and little fingers of the left hand. The cork and wire of the 

 swab-tube are now withdrawn, and the cotton-wool plug is inserted 

 into the culture-tube, and passed onwards until it reaches the 

 sloped surface of the medium. It is then rubbed gently on the 

 latter, and twisted round and round so that every part of the swab 

 may come into contact with the medium. If there is a piece of 

 membrane special care should be taken to see that it is rubbed 

 on the surface, for it is here that we are most likely to find 

 the bacilli. The swab is now withdrawn and replaced in the 

 tube, and the cotton-wool plug of the culture-tube singed and 

 replaced. 



The tube thus inoculated must now be incubated for about 

 eighteen hours at a temperature not exceeding 37° C, and is then 

 ready for examination. 



Hewlett has suggested a useful method which may be carried 

 out without any special apparatus, the white of a hard-boiled egg 

 being used as the culture medium. Take a fresh egg and boil it 

 for ten minutes or more, and allow it to cool. Now take a 

 narrow-mouthed wineglass (or a wide-mouthed bottle, which is 

 better), and rinse it out with perchloride of mercury lotion. 

 Sterilize a knife by passing it slowly through the flame, and cut 

 off the top of the egg, care being taken not to cut into the yolk. 

 Invert the egg into the wineglass (which must be narrow enough 

 to prevent the egg from dropping down into it), taking care that 

 none of the lotion touches the cut surface. This is the culture 

 medium, and it is sterilized ready for inoculation. At a pinch 

 it may be incubated in a warm corner near the fire, near the hot- 

 water cistern, or other warm place. 



