Some problems connected with the Dick test / by R,A, O'Brien and C.C. Okell.
- O'Brien, Richard Alfred, 1878-1970.
- Date:
- 1925.]
Licence: In copyright
Credit: Some problems connected with the Dick test / by R,A, O'Brien and C.C. Okell. Source: Wellcome Collection.
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![SOME PROBLEMS CONNECTED WITH THE DICK TEST. We know from the results of recent work in England, which broadly agree with those obtained in America, that the Dick toxin with which we are working is specifically related to the scarlet fever prevalent here. In the first few days of the disease a suitable dilution of the toxin will give a high percentage of positive reactions; these same patients will during convalescence change their reaction from positive to negative ; the toxin is neutralised by the serum of patients convalescent from scarlet fever, and the toxin, if given in sufficiently large doses to volunteers, will produce what is in some essential characteristics (temperature, vomiting, and rash) a miniature attack of scarlet fever. We know also that the serum of horses immunised with this toxin contains an antitoxin giving the specific Schultz-Charlton reaction. We may go further and say that the accumulating evidence leaves little doubt that, at least in certain severely toxic cases of the disease, the antitoxin has a definite therapeutic effect. There are, however, a great many points still unexplained, and it is by the close study of these that progress will be made. It is necessary to avoid changes in toxin while doing experimental work ; one must, therefore, have a large volume of liquid toxin available. Scarlet fever toxin is strikingly resistant to heat, and of a much higher order of stability than other well-known bacteria] toxins. It is not known at present whether dried toxin, or toxin precipitated by one of the well recog¬ nised methods of precipitation, would be more stable than the liquid toxin. Presumably it would be. The Question of Dilution. We know fairly closely what are the most suitable dilutions of toxins for use. The question is an interesting one. As Park has pointed out: “ If a toxin is a little too strong there will be too many positives; if it is too weak there is a possibility of having people who are susceptible pronounced as immune.” We commenced working with a dilution of 1/6000 of our large bulk of toxin, for with this dilution several of the laboratory staff gave clear positive reactions. Several physicians in fever hospitals have kindly compared the two dilutions 1/6000 and 1/1000. One worker found in the first week of scarlet fever 12 per cent, of positive reactions with dilution 1/6000,](https://iiif.wellcomecollection.org/image/b30625257_0003.jp2/full/800%2C/0/default.jpg)
