Abstract
The non-pathogenic tetragenous ameba described here multiplies in the intestine of man, without producing any noticeable symptoms of dysentery. This non-pathogenic ameba is distinguished morphologically and biologically from Entamoeba tetragena Viereck and Entamoeba coli Lösch emend. Schaudinn. The vegetative forms of the non-pathogenic tetragenous ameba may be divided into two groups, large and small. The large vegetative form is found in the normally evacuated or the diarrheal stools obtained after purgation. The small form is found in the soft stools. This form may be transformed into cysts, or may reproduce itself by binary fission. Cysts are found in relatively large numbers in the soft and formed stools. Experimentally, the new tetragenous ameba may be readily distinguished from the pathogenic variety. The vegetative forms of the dysentery ameba produced the disease in 91 per cent of cases when introduced per anum, and in 50 per cent where the cysts were introduced per os. Similar infection experiments undertaken on twenty-three young cats, i.e. ten experiments with the vegetative form of the non-pathogenic tetragenous ameba per anum, and thirteen experiments with the cysts per os, failed to produce pathological conditions. The intestines of the animals macroscopically and histologically failed to show any of the changes of dysentery. Hence we may conclude that the new type of tetragenous ameba described here is non-pathogenic for man and for young cats.