206 



SCIENCE 



[N. S. Vol. XXV. No. 632 



mucous surfaces with -which the parasite 

 usually comes in contact are of all parts 

 of the body the most susceptible to injury 

 in this fashion, and, as we shall see later, 

 many parasites combine with the mechan- 

 ical lacerations of tissue by movements and 

 their hold-fast organs, a physiological in- 

 fluence of far-reaching import. 



A complicated case which indicates the 

 combined effects of mass and motion, with 

 possibly additional features of a physio- 

 logical character not yet well understood, is 

 illustrated by the smaller liver flukes of the 

 genus Opisthorchis. These species occur in 

 the gall ducts of the liver and there they 

 evoke changes which, though radical, are in 

 general uniform for different species and 

 hosts. As the flukes advance into the finer 

 canals of the liver, the ducts become com- 

 pletely occluded. The first result is bile 

 stasis and consequent dilation of the canal 

 until this acquires considerable size. Both 

 the epithelial layer and the connective 

 tissue of its wall undergo profound modi- 

 fications. The epithelium shows an active 

 catarrhal irritation. The glands manifest 

 considerable hypertrophy. Many new ac- 

 cessory ducts are formed alongside the 

 original one. Among the secondary effects 

 one may note that while the connective 

 tissue proliferates actively and acquires 

 enormous thickness, the liver tissue under- 

 goes granular degeneration as the cells 

 gradually atrophy, thus the functional por- 

 tion of the organ is gradually replaced by 

 inert tissue. The arrest of the bile is fol- 

 lowed by digestive disturbances and com- 

 pression of the branches of the portal vein 

 produces venous stasis, from which follows 

 naturally the ascites so frequently observed 

 in the course of the malady. Now all of 

 these modifications follow the mechanical 

 stoppage of the duct naturally, though no 

 doubt the effect is increased by the irrita- 

 tion produced by ■ the movements of the 

 parasites. Some investigators hold that 



the flukes feed upon the mucous lining of 

 the ducts ; this is true of other liver flukes, 

 but according to my observations does not 

 apply to Opisthorchis. 



Parasites, however, not only carry on 

 movements through their natural territory, 

 but they also from time to time indulge 

 in migrations, the causes of which are not 

 clear, but the effects are serious in the 

 extreme. 



The extent of such abnormal migrations 

 is well illustrated by Ascaris lumhricoides. 

 This form has been known to migrate along 

 evident pathways from the duodenum into 

 the biliary ducts, and liver, where it has 

 induced hepatic abscesses, or into the pan- 

 creas with like results, into the larynx and 

 trachea with the result of suffocating the 

 host, into the eustachian tube to emerge 

 from the auditory canal after perforating 

 the tympanic membrane, or even into the 

 frontal sinuses, or the internal angle of the 

 eye. 



Such erratic parasites do not always con- 

 fine themselves to normal passageways of 

 the body. Even where the penetration of 

 tissue is distinctly exceptional, it not infre- 

 quently happens that under some unknown 

 stimulus the species brings itself to trans- 

 gress natural limitations and to open an 

 abnormal communication between regions 

 otherwise entirely separated. Asearids 

 have perforated the intestine, penetrating 

 the peritoneal cavity, have come out from 

 abscesses at various points, or have been 

 discovered on the occasion of a post-mortem 

 in the most varied regions of the body. 

 The liver fluke as it feeds upon the hepatic 

 cells may chance to open a small vessel, or 

 the lung fluke may similarly effect an en- 

 trance into the circulatory system and 

 either be thus carried into distant and un- 

 natural parts of the body, reappearing in 

 abscesses, and in expansions of the eyelids, 

 or being caught in brain tumors, which 

 sooner or later arouse the disturbances that 



