In a paper published last year, I described the female, nymph and larva of Ixodes caledonicus. Having regard to the views expressed in my recent paper on the adaptation of ticks to the habits of their hosts, I wrote to Mr William Evans, in Edinburgh, asking him, if possible, to kindly search the dove-cot at Dunipace, Stirlingshire, for the missing male which he would probably find in the habitat of the host, the domestic pigeon. On 25 May, 1911, Mr Evans discovered two ticks, a male and female in copula, in the dove-cot, and he sent the specimens to me for identification. The female accords with my published description of caledonicus. The male is here described for the first time, and it is interesting to find that it agrees in structure and habits with what was to be expected according to the theory advanced by me in the second paper I have referred to.

In the following pages an attempt has been made to give a short summary of our knowledge of the Relapsing Fever of Tropical Africa, and also to include the results of my own experiments and observations on this disease. The literature on the subject is already somewhat considerable and widely scattered, therefore no apology is needed for bringing it together.

Dysentery is usually classified as (i) bacillary, and (ii) amoebic.

In 1898 Shiga described a bacillus (B. dysenteriae, also known as Shiga's bacillus), as the cause of epidemic dysentery in Japan. Since then his observations have been, in the main, confirmed. Other varieties of dysentery bacilli have been described and “Bacillary Dysentery” seems now to be a well-defined disease capable of study by ordinary bacteriological methods.

The following is a brief description of a blood worm which was first observed by Mr J. W. Kehoe, one of the technical assistants at the Federal Laboratory. The parasite has been found in squirrels coming from almost all parts of California east of the Sierra Nevada Mountains, and between the Mexican border and the Sacramento River (between 33° and 38° North Latitude).

1. The parasite described inhabits the alimentary tract of two species of Lucilia. In addition it has a resting stage—the ‘cyst’—which is passed in the voided excrement of the insect.

2. When the cyst is ingested by a fly it grows in length and becomes flagellated in the ‘crop’; in the midgut it greatly elongates and multiplies rapidly by division; in the hindgut it first shortens, then becomes spherical, and finally oval and cyst-like, meanwhile losing its flagellum.

3. The cysts measure 3 μ, the fully flagellate forms 20 μ, in length.

4. The cysts possess a cytostome and cytopharynx, the functions of which are probably nutritive.

5. The flagellum consists of two parts (i) a cytoplasmic part, which probably subserves the power of movement and which I therefore propose to call the kinetoplasm, and (ii) a thread of chromatin secreted by the rhizoplast.

6. The function of the chromatin in the flagellum is probably to sustain a filamentous form.

7. The nucleus divides by a definite process something akin to mitosis.

8. The chromidia serve as reserve material for the supply of chromatin in the cell. They are secreted probably by cell-plastids.

9. I propose the name of this parasite be Herpetomonas luciliae, and that the genus Herpetomonas should be defined so as to include the forms described as Leptomonas.

1. Crithidia pulicis, n. sp., is a parasite of the alimentary tract of the human flea, Pulex irritans.

2. The fleas used in this investigation were bred to the third generation in special “flea cages” on the human body. “Wild” fleas were examined and yielded the same parasite. Both larvae and adult fleas were examined.

3. C. pulicis exhibits pre-flagellate, flagellate and post-flagellate stages in its life history and these phases gradually develop, the one from the other.

4. The flagellate form is very active, movement being accomplished by means of the myonemes of the membrane and body.

5. Pre-flagellates (figs. 1−8) are oval bodies, from 2·3 μ to 7 μ long by 1·5 μ to 4·5 μ broad. The nucleus contains much chromatin and a small karyosome may be present. The blepharoplast is large. The flagellum develops from a chromatophile area. The rate of acquisition of flagellum and membrane varies in individual parasites. Division rosettes are frequent. The pre-flagellates have a somewhat frail appearance.

6. The flagellates of C. pulicis (figs. 9−17) are 26 μ to 65 μ long. Their cytoplasm is richly but finely granular, the nucleus well marked, the blepharoplast large, showing slight variations in shape. Chromidia may be present. The undulating membrane is large, well marked and possesses myonemes which can be detected in the living organism. The free flagellum is relatively short.

7. Post-flagellates (figs. 23−36) are from 3 μ to 6 μ. by 2·0 μ to 4·6 μ. They occur in the rectum and dejecta of the fleas. They are produced by concentration of the protoplasm round the nucleus and blepharoplast with absorption of the membrane and flagellum and finally the production of a thin varnish-like coat.

8. Longitudinal division (figs. 15−22) is the method of multiplication. It occurs in the pre-flagellate and flagellate stages. It may be symmetrical or asymmetric. Division is initiated by that of the blepharoplast, followed by that of the flagellum, membrane and nucleus and finally the body cytoplasm. Two types of asymmetric division have been observed.

9. The method of infection is contaminative, the post-flagellates in the faeces being the source of infection. There is no evidence of hereditary infection.

10. Crithidia pulicis is a member of the genus Crithidia, and is a true parasite of the insect, Pulex irritans.

By many observers Negri bodies have been considered to be parasitic in nature (Negri, 1903; Babes, 1907). Williams and Lowden (1906) go further and describe the life cycle of these bodies, regarding them as belonging to the Sporozoa, and give to them the name of Neuroryctes hydrophobiae. Calkins (1910), although he states that the parasitic nature of these bodies is not proven, still evidently inclines to that view. In his criticism of the work of Williams and Lowden he comes to differ from them as regards the classification of the supposed organisms. He thinks that their variable forms, the uninucleate condition, the occurrence of a state of distributed chromatin, and the budding phenomenon, are characteristic not of Sporozoa but of parasitic Rhizopods. His opinion is that the distributed chromatin masses in the Negri bodies are in all probability representative of the idiochromidia which are so characteristic of Rhizopods.

The present report is an account of observations made in Bagdad during the year 1910 (March to November) on the Oriental Sore as it occurs in this part of the world. Though the sore of Bagdad may not differ very markedly from that of other places, it is so common here that all stages and types of the sore may easily be studied, and such points as the early age of infection, immunity, and duration of the disease are very clearly exemplified. Accordingly, a more or less complete account of this disease of Bagdad, known locally as the Date boil or Arabic “Uchut,” will be given, though descriptions of the sore as it occurs in several parts of the world have been published by other observers. During the investigations various side issues arose, and as these suggest certain interesting points, three sections have been added dealing with (1) the life history of Lankesteria culicis (Ross) a gregarine of Stegomyia fasciata, (2) Haemogregarina canis and its development both in the dog and the tick Rhipicephalus sanguineus, and (3) Her-petomonas muscae domesticae, and other flagellates of the house-fly.