Laboratory Diagnosis.—The mucoid mass of amoebic dysentery is often brownish. The pathogenic amoeba shows active finger-like processes and in acute attacks often shows contained red cells. In the fresh specimen of the milky mucopurulent mass of bacillary dysentery one observes large numbers of pus cells and particularly very large phagocytic cells which greatly resemble amoebae. Upon staining with Gram’s stain one may find numerous Gram-negative bacilli in the cytoplasm of this cell.
These large cells which resemble amoebae are often vacuolated, thus intensifying the similarity. They are nonmotile, however, and do not show the small ring nucleus which is so characteristic of the vegetative human amoebae. The nucleus of the confusing cells is also larger, approximating one-fourth the size of the cell.
Bacillary dysentery stools show an absence of Charcot-Leyden crystals which are often present with amoebic stools.
For bringing out the nuclear characteristics of human amoebae Walker recommends fixation of thin moist smears in Giemsa’s sublimate alcohol (absolute alcohol 1 part, sat. aq. sol. bichloride 2 parts) for 10 to 15 minutes. These smears are then well washed with water and stained with alum haematoxylin for five minutes. The nuclear characteristics are noted under etiology. In such staining the preparations, which are best made on cover-slips, should never be allowed to become dry.
An excellent iron haematoxylin method is that of Rosenbusch:
Rapidly smear out with a toothpick a small particle of faeces or other material containing protozoa and, while still moist, fix by Giemsa’s method and, after getting rid of the mercury with iodine solution followed by 95% alcohol, treat smears with a 3.5% solution of iron-alum in distilled water for one-half hour or overnight, then wash thoroughly in distilled water.
Then stain from five to twenty minutes in the following haematoxylin stain: (1) 1% solution of haematoxylin in 95% alcohol. It takes at least ten days to ripen. (2) A saturated solution of lithium carbonate. Add to 10 cc. of the haematoxylin solution 5 to 6 drops of the lithium carbonate one. Next wash well and differentiate with about 1% solution of the iron-alum. Again wash in water, pass through alcohols to xylol and mount in balsam. With vegetative amoebae I have obtained beautiful results with vital staining which can best be done by tinging the faeces emulsion with a 1% aqueous solution of neutral red. I have also had good results by emulsifying the faeces in a drop of 1 or 2% formalin and then adding a drop of 2% acetic acid. The mixture is then tinged with either neutral red or methyl green.
For distinguishing the encysted form of Entamoeba coli one can obtain excellent results by emulsifying the faeces in Gram’s iodine solution. Owing to the glycogenic reaction given by E. coli, the round amoeba, with its 8 nuclei stands out very distinctly.
For diagnosing the 4-nucleated cyst of the pathogenic amoeba one gets better results with haematoxylin as this brings out not only the 4 nuclei but the chromidial bodies as well. It was formerly customary to recommend the administration of salts prior to examining for amoebae. Walker warns that such a procedure gives us amoebae which are difficult to differentiate, the nuclear characteristics of E. coli and the tetragena nucleus of E. histolytica being much alike as they both contain much chromatin. In a dysenteric stool the histolytica type of nucleus, containing but little chromatin, does not resemble the nucleus of E. coli.
He prefers the examination of formed stools obtained without a purgative.