ENTOZOA IN THE ALIMENTARY CANAL. 65 



sometimes exists) may be regarded as a pathognomonic 

 sign of the presence of one of those species of worms 

 in the intestinal canal ; but some species of entozoa, 

 and the ova of all the intestinal worms, can only be 

 detected by means of a microscopic examination. 



The affections produced by the existence of intes- 

 tinal entozoa do not, in general, follow a regular 

 course. They very often make their appearance sud- 

 denly, and are followed by remissions of variable 

 length, and, frequently also, there is some predomi- 

 nant symptom of an unusual character, which comes 

 on unexpectedly and goes away again without any 

 apparent cause, and at no certam period ; whilst the 

 symptoms bear no relation to one another. 



When the entozoa leave the intestines and pass 

 into other organs, either through natural or acci- 

 dentally-formed passages, they often give rise to new 

 symptoms or complications. 



The entozoa which are observed in the human 

 intestines belong to the protozoa, and to the cestoid, 

 trematode, and nematoid classes of worms. Several 

 species have only been met with once, or upon very 

 few occasions. 



To the protozoa the following belong : — The vibrio, 

 the cercomonas hominis, and the paramecium coli. 



The cestoid intestinal worms are : — The taenia 

 sohum, the bothriocephalus latus, and the taenia nana. 



The only trematode worm found in the intestines 

 is the distomum heterophyes. 



The nematoid intestinal worms are : — The anchy- 

 lostomum duodenale, the ascaris lumbricoides, the 

 ascaris alata, the tricocephalus dispar, and the oxyuris 

 vermicularis. 



