202 PARASITES OF MAN 



parasite for injury. Where the entozoa are of minute size, 

 and where their injurious action is primarily due to the 

 mechanical obstructions they set up, it is clear that the 

 virulence of the helminthiases, or resulting diseased conditions, 

 will mainly depend upon the number of intruders. 



Another consideration of the highest value in relation to 

 epidemiology generally, and more especially in regard to the 

 practical question as to the best methods of stamping out para- 

 sitic plagues, is that which refers to the life-history of the 

 entozoon itself. It must be obvious that in all cases where the 

 intermediate host can be captured and destroyed, the life-cycle 

 of the parasite can be broken and interrupted, and if thus 

 broken, there is an end to the further propagation of the 

 species. The knowledge that we have acquired by experi- 

 mental research in this connection has already enabled us to 

 set a limit upon the prevalence of certain well-known disorders, 

 such as Trichinosis, Cestode-tuberculosis, and so forth. In 

 the case of epizootics, however, which are indirectly due to the 

 action of intermediary hosts that cannot be readily captured or 

 destroyed, then our power of arresting the disease is com- 

 paratively limited. In the present case it is probably not 

 necessary either that a dead or living mosquito should be 

 swallowed to insure infection ; but it is necessary that the 

 parasitic larvae should have dwelt within the mosquito in 

 order to arrive at the highest stage of larval growth prior to 

 their re-entrance within the human territory. Undoubtedly, 

 the larvae are swallowed with potable waters. Perfect filtra- 

 tion before use would certainly check, if in course of time it 

 did not totally extinguish several of the many virulent diseases 

 that now afflict the inhabitants of warm climates. 



It is with reluctance that I terminate this article, but in 

 the closing pages of this work (Book II, Section V) I hope 

 to add a few more particulars in reference to Lewis's latest 

 researches. 



BIBLIOGRAPHY (No. 23). Araitjo, A. J. P. da Silva, "Me- 

 moria sobre a Filariose," &c., Bahia, 1875 ; see also ' Arch, de 

 Med. Nav./ 1875 and 1878. Bancroft, J., "Cases of Filarious 

 Disease/' in 'Pathological Soc. Trans/ for 1878, vol. xxix, 

 p. 407. BOUT el- Bonder e, "Resume of and Commentary upon 

 the writings of Silva Lima, Silva Araujo, and others," in 

 ' Arch, de Med. Nav.' for March, 1878. Idem, " Pathologie 

 exotique. De Phematozoaire neinatoide de Fhoinme et de son 



