The writer describes an accurate and reliable method for preparing an iodine stain for use in wet preparations containing intestinal protozoa.
To a 1 per cent standardized potassium iodide solution is added 1.5 grams of powdered iodine crystals per 100 cc., in order to provide an amount of iodine considerably in excess of saturation and to compensate for volatilization. The solution is allowed to stand for 4 days and is then filtered.
To insure success in the preparation of the stain, several points must be observed:
(1)Solutions should be weighed to the fourth decimal place in standardizing the potassium iodide.
(2)Iodine concentration will remain constant only if powdered iodine is used in the solution.
(3)To insure saturation the solution should be allowed to stand for 4 days before it is used.
(4)The solution should always be filtered before being used.
(5)Filtered bottles of solution should be kept in tight, glass-stoppered bottles for periods not exceeding 4 weeks. However, unfiltered stock solutions can remain long periods of time seven if stoppered only lightly, and from these filtered solutions can be made up at a moment's notice.
The advantages of this new standardized iodine stain over those prepared by the older methods now in use may be summed up as follows:
(1)If prepared as outlined above, the stain will be standard wherever prepared.
(2)Once the standardized potassium iodide solution is made up, the method of preparing the stain is the most rapid of any iodine stain now believed to be in use.
(3)The stain shows little or no deterioration over long periods of time.