(1923) of 35.5 per cent. for their series of 1182 mental hospital inmates, but lower than their figure of 61 per cent. in their series of 505 cases. The species was recorded in all age-groups, and as in the case of E. histolytica was found in recent admissions as well as in inmates of long standing in the community. The cysts observed ranged in diameter from 14 microns to 22 microns, were generally spheroidal, although in several stools up to 50 per cent. of the cysts observed were ovoidal, and in one case two sub-cylindrical cysts were found. The majority of infestations were of the medium and large races, ranging from 16 microns to 22 microns. In one stool, both the large and the small races of E. coli were present along with an infestation by the medium race of E. histolytica. E. coli was found commonly in the stools of individuals admitted more than 12 months before examination.

Endolimax nana (Wenyon and O'Connor)

Characteristic cysts of this common commensal amoeboid protozoan were found in stools of two individuals of the faulty group. This total incidence of only 2 per cent. is undoubtedly correlated with the nature of the routine technique employed. The cysts of this species are small, usually only 8 microns to 10 microns in diameter and differentiate poorly with simple iodine preparation. Faust and his associates (1939) have shown that the examination of haematoxylin stained films will reveal 60 per cent. more positives for this species than any other technique; but such films prepared from formalinised material are too variable for consistent results, and we could not make this a routine part of our technique. The actual incidence might normally be anticipated to be between 17 per cent. and 24 per cent.

Iodamoeba butschli (Prowazek).

Cysts of this species were observed in one stool (2.25 per cent.) of the faulty group, and three stools (5.35 per cent.) of individuals of the normal group. This total incidence of 4 per cent. is similar to that of 5.4 per cent. determined as the incidence among 1182 mental hospital cases by Boeck and Stiles (1923), and to that of 6 per cent. recorded by Miller (1939) among the inmates of a children's institute. It is almost half the incidence of 9 per cent. determined by Young and Ham (1941) for their selected group of 142 mental hospital inmates of untidy habits. Few cysts were observed in any of the positive preparations. The cysts were subspherical to ovoidal in shape, ranging from 9 microns to 15 microns on the longer axis, but showed clearly in all cases the peculiar nuclear morphology characteristic of the species. It is quite possible that formalin preservation is not favorable for the cysts of this species, as the present records are with one exception from stools examined fresh.

Giardia intestinalis (Lambl).

Infestations with this flagellate were found in five cases, in three individuals (6.8 per cent.) of the faulty group, and two (3.57 per cent.) of the normal group. The former were young, less than twenty years of age; the latter were in their third and fifth decades. One individual had been admitted less than two months before

examination. In the individuals of the faulty group, large numbers of cysts were being passed. There is a marked age correlation for the determined incidence of this species (Meleney, Bishop, and Leathers, 1932). The incidence of infestation rises to a peak of 25 per cent. between the ages of two and seven years, falls to a minimum of 2.5 per cent. at thirty years, and is maintained near this level in the subsequent age-groups. Miller's (1939) figure of 19 per cent. is high and related to the lower average age of the group he studied. Matthews and Smith (1919) determined an incidence of 3.4 per cent. in mental hospital patients, a figure similar to that of Boeck and Stiles (1923), who record an incidence of 3.1 per cent. for their entire group and of 15.4 per cent. in their group of 505 patients examined six times each. Young and Ham (1941) record an incidence of 6 per cent. in the select group examined by them. The incidence of 5 per cent. recorded here for the whole group agrees well with that of studies elsewhere, and the incidence of 6.8 per cent. for individuals of the faulty group agrees well with that determined by Young and Ham. The cysts observed showed little variation, being mostly 10 microns to 12 microns in length and 6 microns to 8 microns in width. The axostyles and parabasal bodies characteristic of this species in stools from humans were clearly evident.

Trichomonas hominis (Davaine).

The absence of cyst-formation from the life-history of this species limits the detection of Trichomonas infestations to the examination of fresh stools. Many of the fresh specimens examined by us were dry, indurated and unsuitable from the view point of the detection of this species, however in three cases—two of the faulty group (4.5 per cent.), one of the normal group (1.78 per cent.)—this species was observed. The total incidence of 3 per cent. is similar to that of other studies carried out in the present manner; but from the limiting factor mentioned above it is obvious that the results are generally lower than the actual incidence in any group studied.

Chilomastix mesnili (Wenyon).

This species is recorded here on the basis of cysts observed in the stool from one individual of the faulty group. The incidence is exceptionally low and we have no explanation of this since the cysts of this species preserve well and differentiate readily with iodine.

Enterobius vermicularis (Linn.).

Pinworm infestations were recorded in five (11.18 per cent.) of the individuals of faulty habits, and two (3.57 per cent.) of the individuals of normal habits. This total incidence of 7 per cent. is close to that determined by Boeck and Stiles (1923) for their entire group of 1182 inmates of a mental hospital in the District of Columbia, viz., 5.8 per cent. on the basis of an average of 3.2 examinations per person. It contrasts with the negative findings reported for this species by Young and Ham (1941). Reardon (1941) reports 69 per cent. infestation with E. vermicularis in the small group which she examined, but this is the result of examinations by N. I. H. swabs. The present records and those of earlier