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SCIENCE. 



[N. S. Vol. XXII. No. 555. 



tion. The arthropods furnish many car- 

 riers of disease and breeders also, as the 

 extended references already made to these 

 forms suffice to show. The more or less 

 perfectly acquired external parasitism of 

 these forms is admirably adapted to these 

 functions, but such animals are not the 

 immediate cause of disease, and when sick- 

 ness follows a bite of a fly, a spiden or a 

 tick, the effect is more probably due sec- 

 ondarily to the bite and primarily to some 

 other organisms introduced thereby. 



In the case of the parasitic worms the 

 conditions are decidedly changed. Here 

 are species which parasitize within the 

 body, often suck the blood of the host, 

 lacerate delicate mucous membranes, induce 

 internal hemorrhage, in some instances 

 feed upon the cells of the tissues, and 

 destroy important organs or grow to such 

 size as to encroach upon normal structures 

 and functions. In addition to these ana- 

 tomical interferences, some of the parasitic 

 worms are known to produce waste matter 

 in their own biological processes, toxins, 

 which act deleteriously upon the host or- 

 ganism and evoke abnormal and serious 

 symptoms in it. Thus Vaullegeard has 

 isolated experimentally from tapeworms 

 two chemical substances which act upon 

 the blood and nerve and which, injected 

 into experimental animals subcutaneously, 

 produce the epileptic symptoms that char- 

 acterize severe cases of tapeworm infec- 

 tion. Then the physician speaks of a 

 Botliriocephaliis anemia, recognizing a defi- 

 nite group of symptoms, a distinct disease 

 produced by the parasitism in man of the 

 broad fish tapeworm (Dihothriocephalus 

 latus). Here the animal is the immediate 

 cause of the disease and the removal of the 

 tapeworm is followed at once by the disap- 

 pearance of the undesirable symptoms. 



"While there are some animal parasites 

 which are believed to be harmless, or, better 



expressed, do not do any damage to the 

 human system so far as present knowledge 

 extends, yet the studies of recent years 

 have furnished constantly increasing evi- 

 dence of the pathogenic role of these organ- 

 isms. They do damage indirectly by irri- 

 tating the delicate mucous membranes and 

 by lacerating them, thus giving access to 

 the omnipresent bacteria, a danger which 

 has been greatly underrated. But they 

 are also the direct cause of disease which 

 in consequence of their part in its produc- 

 tion the physician names after the species 

 of parasite, as trichinosis, uncinariasis, 

 hydatid disease, etc. Note further that 

 they are not factors of trivial importance 

 in general hygiene or of little bearing upon 

 the welfare of a nation as a whole, and that 

 a large percentage of such diseases can be 

 treated only by preventive medicine. Thus 

 trichinosis, which is caused by eating pork 

 containing living trichinge {Trichinella spi- 

 ralis), is accompanied by a high mortality 

 and even yet is a serious disease in north- 

 ern Geranany; its prophylaxis is, however, 

 exceedingly simple and no one who is care- 

 ful to avoid underdone pork will ever suffer 

 from its attacks. Again, hookworm dis- 

 ease, or uncinariasis, has been shown by 

 the researches of Stiles and others to be 

 very abundant in certain parts of our 

 southern states. The presence in the ali- 

 mentary canal of myriads of minute hem- 

 orrhages caused by the action of these 

 Avorms, results in a chronic anemia which 

 prevents the attainment of physical or 

 mental development, stunting the individ- 

 ual and leaving him, on arrival at years of 

 maturity, little more than a child in body 

 and in intellect. Much of the degeneracy 

 of the poor white trash of the south is due 

 not to inherited defects or to family short- 

 comings so much as to the presence of this 

 parasite, which from early childhood has 

 continually sapped the vitality of the indi- 



