The virulence testing of the diphtheria bacillus and its practical application / by C.c. Okell and H.J. Parish.
- Okell, C. C. (Charles Cyril), 1888-1939.
- Date:
- [1926?]
Licence: In copyright
Credit: The virulence testing of the diphtheria bacillus and its practical application / by C.c. Okell and H.J. Parish. Source: Wellcome Collection.
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![\All Hights reserved] THE VIRULENCE TESTING OF THE DIPHTHERIA BACILLUS AND ITS PRACTICAL APPLICATION. By C. C. OKELL and H. J. PARISH. The Wellcome Physiological Research Laboratories. Precise methods for the diagnosis of diphtheria involving a virulence test are only slowly being adopted by the general public health administration of this country. This is largely due to the trouble and expense entailed in the proper investigation of bacteriological material. The intradermic test on account of its simplicity and relative cheapness offers, in our opinion, a method which could be applied in any properly equipped public health laboratory. The purpose of the present paper is to describe in detail the technique of the intradermic test as we have applied it, and to give numerical results which may be of help in giving precision to certain commonly held views on the epidemiology of the disease. Technique. We have followed the technique of Eagleton and Baxter which is as follows: The swab when received is smeared over the surface of a Loeffler slope, which is then incubated over-night. The following morning a general smear is made from the surface of the slope, and if this proves positive on examination, it is plated out on Loeffler’s medium in Petri dishes. One part of each plate should be thickly implanted. Loeffler slopes which appear negative at 24 hours should be re-incubated, as occasionally they become positive at 48 hours. We have no evidence that longer incubation is of any value. It is sometimes convenient to damp the swab with sterile broth and plate directly from it. The colony of C. difhtheriae is picked from the plate preferably on the 3rd or 4th day of incubation. The colony is then very characteristic, being a circular disc with raised centre, creamy in colour, and with a matt surface. If the bacilli are at all numerous in the implant, the colonies can generally be picked off at an earlier stage, e.g. 48 hours. A difficulty occasionally met with is due to liquefaction of the Loeffler by one of the organisms present. It is then necessary to resort to plain nutrient agar plates, or plates of Douglas’s tellurite medium. The original swab should be kept in a dark place and retained until isolation has been successful, as it may be advisable to replate directly from the original swab if the primary plate is overcrowded. At least two colonies are selected, and sown on Loeffler slopes. Smears are made from the over-night growth of these and stained by Neisser’s method.](https://iiif.wellcomecollection.org/image/b30625919_0003.jp2/full/800%2C/0/default.jpg)
