METAZOA 



553 



Ascarides may cause serious mischief in the pancreas, as observed by 

 Chalmers; and may cause appendicitis, as noted by Blanchard, 

 Metchnikoff, Castellani, and others. 



5. Bacterial Infection caused by the Parasite.— TncA^^ns trichiura 

 may be a harmless parasite in itself, but it is quite capable of intro- 

 ducing bacteria into the mucosa of the vermiform appendix and 

 causing appendicitis, for, as is well known, it burrows in the mucosa. 

 The fever so often found in patients suffering from ankylostomiasis 

 is probably caused by intestinal bacteria entering the small wound 

 produced by the ancylostome. 



This method of producing ill effects upon the host appears to u? 

 to be of the greatest importance in the tropics, and is, we fear, often 

 overlooked. 



5. Migration of the Parasite in the Body —The larvse of Ancylo- 

 stoma as they enter the skin cause a dermatitis known as Cooly itch, 

 sore feet, ground itch, etc., which may be primarily due to the 

 irritation of the worm, or secondarily to bacteria introduced into 

 the skin by its agency. The wanderings of the larvae of Trichinella 

 spiralis through the muscles cause the severe symptoms of trichiniasis. 



Sambon has pointed out that much that is obscure in the patho- 

 genesis of various forms of helminthiasis might be elucidated by a 

 better knowledge of the migrations of the entozoa in their immature 

 stages from the time they attack the host to that of their settlement 

 in their selective anatomical habitat. He believes that many forms 

 do not go directly to the part in which they are usually found, but 

 may take a very different route from that generally accepted, and 

 may even live for a length of time in other structures before reaching 

 such organs as the alimentary canal or nasal fossae, which are only 

 sought in order to enable the young to escape from the host. During 

 these wanderings mechanical injury may be caused to the host, and 

 pathogenic micro-organisms may be carried from one part of the 

 body to another. 



7. The Absorption of Food— Leuckart estimates that a Dibothrio- 

 cephalus latus gives off in a year proglottides to the weight Oi 

 140 grammes; Tcenia saginata, 550 grammes; and Ascaris lumbri- 

 coides, 42 grammes of eggs in the same period. 



If the number of these parasites is great, the drain on the host 

 must be considerable, especially in children who need food for growth. 



8. Toxins.— This subject has already been dealt with (p. 205). 



9. The Condition of the Host.— The condition of the host is also a 

 factor in the diseases produced by these parasites, for though 

 Ascarides may be harmless in a healthy intestine, they may per- 

 forate a typhoid or dysenteric ulcer, or a traumatic lesion of the 

 bowel, and cause fatal peritonitis. 



With regard to the question as to whether parasites ever benefit 

 human beings, reference can be made to the belief that the develop- 

 ment of the Bacillus tuberculosis Koch is delayed by the presence of 

 entozoa in the bowels, a view which, with our Eastern experience, 

 we are unable to support. 



