ABUNDANCE OF PARASITES. 11 



ever opinion may be held whether we regard the presence of parasites 

 in invertebrates as a necessary preliminary to their sojourn in the 

 body of some vertebrate or not the fact remains the same. The 

 abundance of parasites within the Vertebrata may be more or less 

 accounted for by the fact that there are normally several, if not a 

 great number of species found in the same host. 1 Thus, for example, 

 man has more than fifty distinct species of parasites, the dog and the 

 ox some two dozen each, the frog perhaps twenty. These are of 

 course not all found in the same place and under similar condi- 

 tions, but are scattered throughout the various organs and systems. 

 One takes up its abode in the skin, another in the intestines, 

 a third in the connective tissue between the muscles, while others 

 again inhabit the brain or even the eye. No organ or tissue, how- 

 ever remote or concealed, is entirely free from parasites, and it is 

 well known that even the embryo within the body of the mother is 

 occasionally infested by them. What has been already said about the 

 various species of animals, applies equally well to the different 

 organs ; some are more liable than others to be inhabited by parasites. 

 The outer skin of the body and the alimentary canal seem on the 

 whole to contain the greatest number, and this because they are 

 more easy of access: in man more than three-fourths of the total 

 number of parasites are found in these two localities. 



Frequently the distribution of a given parasite is not confined to 

 a single organ. There are numerous examples, however, of this e.g., 

 Trichina spiralis, when encysted, is found only in striated muscle, 

 the sexually mature Cestodes and Echinorhynckus are confined to the 

 intestines, and Phthirius piibis only inhabits those parts of the body 

 that are thickly covered with hair ; but the converse is almost more 

 general. Cysticercus celhdosce, for instance, infests the intermuscular 



at the enormous number, for there were several thousands. This same helminthologist 

 found on another occasion no less than 82 Ligutce in the intestines of a diver, 

 some of which were 6 to 8 ells long and 8 lines broad. Frequently the intestinal worms of 

 an animal belong to several different species. Nathusius ( A rchivf. Naturyesch., Jahrg. iii., 

 Bd. i., p. 53, 1837), took from a single black stork 24 specimens of Filaria labiata from the 

 lungs, 16 Syngamus (Stronyylus) trachcalis from the trachea, more than 100 Spiroptera alata 

 from the coats of the stomach, several hundred Holostomum excavatum from the small 

 intestine, and about a hundred Distoma ferox from the intestine, 22 specimens of Distoma 

 Itians from the oesophagus, 5 Distoma ( D. hians ?) from between the coats of the stomach, 

 and 1 Distoma echinatum from the small intestine. This forms quite a helminthological 

 museum ; but Krause of Belgrade found even a greater number in a horse two years 

 old over 500 Ascaris mcyalocephala, 190 Oxyuris curvula, several millions of Slronyylus 

 Mracantlius, 214 Sclerostomum arrnatum, 69 Tcenia perfoliata, 287 Filaria papillosa, and 

 6 Cysticerci f (See van Beneden, "Animal Parasites," p. 91.) 



1 Von Linstow has recently published a useful compilation of the distribution of 

 Helminths, which is the most complete in existence : " Compendium der Helminthologie, " 

 Hanover, 1878. 



