172 ~ GARRISON. 



its significance. We are not aware of the previous occupation of the in- 

 dividual in whom Andrews encountered the parasite, but his residence 

 in Manila could scarcely fail to afford opportunity for infection about 

 the ships and docks of the harbor and river, if such situations are the 

 home of the intermediate host of the cestode. However, the Manila 

 case taken alone would seem to lend itself to almost any hypothesis re- 

 garding the source of infection, whether the intermediate host be an 

 insect, moUusk, or fish; and, when taken together with- our knowledge 

 of the earlier cases, the fact that Manila is a seaport- with a harbor and 

 river full of docks and shipping surely strengthens rather than weakens 

 the apparent relations which have been noted between infection with 

 D. madagascariensis and maritime surroundings. 



. So far as we are aware no one has suggested any more plausible 

 theory regarding the source of infection with this cestode than that of 

 Blanchard, namely, that the intermediate host of the parasite is probably 

 some animal of general tropical distribution particularly infesting ships 

 and docks, and that the cockroach {Periplaneta orientalis) would fulfill 

 these conditions. This theory is based in part, of course, upon the 

 analogy presented by the known life cycles of other species of Davainea, 

 the larval forms of which live in arthropods or moUusks. 



The question as to whether D. madagascariensis is normally parasitic 

 in man, or is accidental, having as its normal host some other animal, is 

 naturally suggested by its comparatively rare occurrence in man and by 

 the further fact that species of Davainea are so common in birds and so 

 rare in other animals that it is considered distinctly a bird genus among 

 parasites. But in 1899 Blanchard pointed out that while the great 

 majority of species of this genus were parasites of birds, some five 

 species were then known to be parasitic in mammals,* namely, three 

 in rodents, one in the ant eater, and one in man, and he unlaesitatingly 

 expressed his opinion that D. madagascariensis was a noiTnal and not 

 an accidental parasite of man. That the species has now been found 

 in man ten times and has not. been reported from any other host during 

 a period of over forty years of active helminthological research would 

 seem to render it reasonably certain that we have in Davainea madagas- 

 cariensis a parasite normal, and perhaps peculiar, to the genus Homo. 



BIBLIOGRAPHY. 



Blanchard. Note sur quelques vers parasites de rhomme. Compt. rend. Soc. 



Mol., Paris (1891), 43, 604-615. 

 Idem. Le Davainea madagascariensis a la Guyane. Bull. Acad. med. (1897), 



37, 34-38. 



^ Dr. Ransom informs me that one or two of the mammalian species quoted 

 by Blanchard are probably not true Davaineas, but that a number of new species 

 of Davainea in mammals have since been reported. 



