270 THE DIPHTHERIA BACILLUS 



sore throat, especially if any trace of a false membrane be present, has to be 

 determined by bacteriological investigation. 



By this means it can be ascertained whether any given case of croup or 

 sore throat be the result of an infection with the diphtheria bacillus either 

 alone or in association with other organisms. If a diphtheria bacillus be 

 found, its virulence should be ascertained ; but this is not a matter of great 

 importance in practice, because as a rule it may be assumed that the long 

 bacillus is the most virulent of all the varieties of the diphtheria bacillus 

 and so the virulence of the strain under examination may be gauged from the 

 relative number, or entire absence, of such forms and because from the 

 point of view of treatment the mere fact that the diphtheria bacillus has 

 been found demands the administration of antitoxin. 



When dealing with a case of sore throat three investigations are necessary 

 before the bacteriological examination can be said to be scientifically complete. 

 First films from the inflamed surface must be examined, then cultures must 

 be sown with the material from the throat, and lastly the causal organism 

 must be isolated and injected into an animal. In clinical work, however, 

 the two former investigations are all that is required and these occupy 24 

 hours at the outside. 



1. Collection of the material. 



Remove the false membrane on a small piece of absorbent cotton-wool 

 fixed in a pair of pressure forceps : in those cases in which the membrane is 

 very adherent it is better to tear it off with the forceps. For the collection 

 of material in the ordinary way it is convenient to have a small cotton-wool 

 plug fixed on the end of a metal rod ; this is placed in a test-tube which is then 

 plugged with wool and the whole sterilized in the hot air sterilizer. If there 

 be no membrane scrape the surface of the tonsils or pharynx with a small 

 platinum or nickel spatula. 



When it is desired to send a fragment of false membrane to a laboratory situated at a 

 distance, place it in a small sterilized tube plugged with wool ; or wrap it in a piece of 

 thin cloth which has been passed through boiling water and then place it in a new glass 

 tube carefully plugged. 



Most laboratories send the necessary apparatus for the collection of material to prac- 

 titioners. A convenient form is that which contains two sterilized plugs in test-tubes, 

 a sterile tube for false membrane and a small spatula, as well as two tubes of serum. 



2. Methods of examination. 



A. Microscopical examination of the fresh material. This part of the 

 investigation is of considerable importance. 



Before using the false membrane for bacteriological examination press it 

 lightly between sterile filter-paper to blot up any mucus which may be present 

 on the surface. 



1. Prepare films with small portions of the exudate, and stain with Roux's 

 blue, wash and dry. Examine with an oil immersion lens. [Cobbett's method 

 (p. 252) is recommended as giving more characteristic appearances.] 



The absence of the diphtheria bacillus must not be assumed if the micro- 

 scopical examination be negative as it is a well known fact that it often passes 

 unrecognized when mixed with a number of other organisms (Martin). 



Should bacilli resembling diphtheria bacilli be found in the preparation, 

 the diagnosis may be advanced a stage by staining other films by Gram's 

 method. The diphtheria bacillus is gram-positive, and a certain number 

 of bacilli frequently found in the mouth and morphologically resembling it, 

 but gram-negative, can by this means be excluded. 



Cultures must be sown in every case. 



