The structure and life history ofCrithidia pulicis, n. sp., parasitic in the alimentary tract of the human flea,pulex irritans

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Abstract
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. pulicisexhibits 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 ofC. 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 pulicisis a member of the genusCrithidia, and is a true parasite of the insect,Pulex irritans.
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