The application of the eosin-eriterion for the viability of protozoan cysts to cysts of Hartmanella hyalina treated with chlorine-water.

Abstract

Owing to the fact that no satisfactory method has been developed to induce the excystment and growth of the amebse parasitic in the human intestinal tract, no absolute criterion has been established to distinguish the viable from the non-viable cysts. The penetration of the cysts by analine dyes is regarded as an indication that the cysts are dead and the use of eosin as an indicator has been generally accepted. The ultimate fate of the cysts which fail to take the eosin stain has not been finally determined. It has been shown that cysts which undergo a plasmolysis may not stain red by the eosin, though they are considered to be incapable of development. The present investigation was undertaken in order to determine the percentage of free chlorine in water necessary to retard the development of cysts of Hartmanella hyalina and at the same time to determine the fate of the cysts which presented an apparently normal appearance. It is hoped that by comparing the resistance of the cysts of the human intestinal Protozoa with the resistance of the coprozoic ameba under consideration that information may be procured regarding the relative value of methods employed in disinfecting fruits and vegetables for table use and regarding the general resistance of Protozoan cysts. Cysts of Hartmanella hyalina were placed in water containing different percentages of free chlorine in solution. A ten minute interval was allowed before the cysts were transferred to a suitable culture medium which in this investigation was 10 per cent horse serum in Locke's solution diluted with 50 per cent distilled water. The cysts were counted at the time of their transfer to the culture medium and the reaction of a representative number of the cysts to Donaldson's iodine-eosin was noted.