568 THE MICROSCOPE. 



of fluke, discovered by Dr. Bilharz in the human portal 

 system of blood vessels, gives rise to a very serious state of 

 disease among the people of Egypt. So common is the 

 occurrence of this worm, that this physician expressed his 

 belief that half the grown-up people are infested with it. 

 Griesiuger conjectures that the young of the parasite exists 

 in the waters of the Nile, and in the fishes which abound 

 therein. Dr. Cobbold thinks " it more probable that the 

 larvae, in the form of cercariae, rediae, and sporocysts, will 

 be found in certain gasteropod moliusca proper to the 

 locality." The anatomy of this fluke is fully described in 

 Kuchenmeister's able work on Parasites, by Leuckart, and 

 by Cobbold. The eggs and embryos of Bilharzia are 

 peculiar in possessing the power of altering their forms in 

 both stages of life ; and it is more than probable that the 

 embryo form has been mistaken for some extraordinary 

 form of ciliated infusorial animalcule, their movements 

 being most quick and lively. We cannot fail to notice 

 the curious leech-like form of the male animal, and, re- 

 markable enough, he is generally found carrying the female 

 about. The whip-like appendage seen in the figure is a 

 portion of the body of the female. The disease produced 

 by them is said to be more virulent in the summer months, 

 which is probably owing to the prevalence of the cercarian 

 larvae at the spring time of the year. 



Trichina spiralis. — This, the smallest of the helminths, 

 measures only the l-20th of an inch. The female is a little 

 larger ; it was discovered by Professor Owen in a portion 

 of the human muscle sent to him from St. Bartholemew's 

 Hospital, 1834. The young animal presents the form of 

 a spirally- coiled worm in the interior of a minute oval- 

 shaped cyst (Plate IV. No. 104), a very small speck 

 scarcely visible to the naked eye. In the muscle it resem- 

 bles a little particle of millet seed, more or less calcareous 

 in its composition. The history of the development of 

 Trichinae in the human muscle is briefly that in a few 

 hours after the ingestion of diseased flesh, Trichinae, dis- 

 engaged from the muscle, are found free in the stomach : 

 they pass thence into the duodenum, and afterwards 

 advance still further into the small intestine, where they 

 become developed. Prom the third or fourth day, ova or 



