DIPHTHERIA 43 



shall defer the description of the points upon which a diagnosis 

 is to be based until we deal with the examination of cultures. 



CULTURAL METHODS. 



The diphtheria bacillus grows best at or near the body tem- 

 perature (about 37 C), and flourishes on almost all culture 

 media. But agar is scarcely ever used in growing* it for diag- 

 nostic 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 develop- 

 ment 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 The cork and wire of the swab-tube are now withdrawn, and 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 this also is inocu- 

 lated, 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 The swab is now withdrawn and replaced in the tube, and the 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 car- 

 ried 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 



