214 



SCIENCE 



[N. S. Vol. XXV. Xo. 632 



primary effect upon the functional process 

 of the organ is directly related to the num- 

 ber of such injuries, or, in other words, to 

 the number of parasites at work. Other 

 parasites burrow into the intestinal wall 

 and produce there nodules of various sorts. 

 Nematodes particularly determine the for- 

 mation of such nodules in various organs 

 of the host.° These nodules may be of con- 

 siderable size, but in any event they in- 

 volve the destruction of some functional 

 tissue and the consequent impairment of 

 the functional activity of the organ. 



Among the physiological activities of 

 parasites none is more striking in its reac- 

 tion upon the economy of the host than the 

 power that has been acquired by some 

 forms which live upon blood to secrete a 

 substance that inhibits the coagulation of 

 the blood. Leo Loeb and Smith have re- 

 cently shown that the hook worm secretes 

 in glands of the anterior body region a sub- 

 stance which is exceedingly effective in in- 

 hibiting the coagulation of blood. This is 

 antagonistic to the normal reaction of the 

 mucosa. Consequently the points at which 

 these parasites have attached themselves to 

 the membrane become seats of continued 

 hemorrhage, and in case of a numerous in- 

 fection by the species there are myriads of 

 minute hemorrhages constantly discharging 

 blood' into the cavity of the canal. The 



" Thus Selerostoma equinum produces tumors on 

 the intestinal lining of the horse; Spiroptera 

 megastoma in the submucosa of the horse; Spirop- 

 tera sanguinolenta in various organs of the dog, 

 fox, etc.; (Esophagostoma columbianuni in the 

 intestine of sheep; Strongylus Ostertagi in the 

 fourth stomach of cattle; Gnathostoma siamense 

 in the subcutaneous tissue of man. 



' As a matter of fact Looss has demonstrated 

 that blood is not the normal food of the hook 

 worm, as these parasites feed on the mucous 

 membrane of the host, and blojd is sucked in 

 only when the parasite accidentally pierces a 

 vessel. Looss takes the position that a toxin is 

 produced which acts hemolytically, pointing out 

 the fact that in some fatal cases of severe anemia 



powerful anemia which is associated with 

 the parasitism of the hook worm receives 

 in this way a ready explanation. 



There are many eases in which produc- 

 tion of diseased conditions in the host ap- 

 pears distinctly traceable to the presence 

 of a parasite and removable by the removal 

 of the parasite. These diseased conditions 

 are general, not local. They are appar- 

 ently due to some abnormal stimulation 

 and have usually been explained on the 

 basis of the influence of toxic materials 

 which the parasite produces. That para- 

 sitic organisms, like all other animals, pro- 

 duce waste matter and give it off into the 

 fluids by which they are surrounded is not 

 open to question. If the view already ad- 

 vanced of the active metabolism carried out 

 by the parasites, and if the extremely high- 

 ly developed excretory system are correct 

 indications, then the amount of such waste 

 material eliminated would be proportion- 

 ately large. It is also undoubtedly true 

 that various investigators have been able 

 chemically to isolate toxic principles from 

 the bodies of various parasites, and that in 

 a number of instances these substances have 

 been tested in their effects on living organ- 

 isms with the result of producing changes 

 or invoking symptoms distinctly analogous 

 to those which have been recorded as the 

 consequences of infection by the specific 

 parasite. It also appears that the evidence 

 which has been collected heretofore seems 

 to indicate a difference in the degree of 

 the effect exercised by living and by dead 

 helminthes, for the latter are much more 



the number of parasites found in the intestine waa 

 too few to explain the severity of the illness. It 

 does not seem to me to be necessary t ) infer the 

 production of some unknown toxin, since the 

 possession of a secretion inhibiting the coagula- 

 tion of the blood would account for the persistence 

 of the hemorrhages, and it is this factor of con- 

 tinuance which makes of them dangerous ele- 

 ments. It is well knoi\Ti that the leech also pro- 

 duces such a substance in its glands. 



