FILARIA LOA 113 



smooth and does not show the markings and irregulari- 

 ties that occur in elephantiasis. Embryos, if found 

 in these infections, are sheathed and have a diurnal 

 periodicity Microfilaria diurna. Manson suggests that 

 these swellings are caused by the parturition of an adult 

 female at the site of the swelling. So far this has not 

 been proved, but in one case a worm appeared on the 

 surface of such a swelling. 



Eosinophilia is marked in infections with this worm. 

 Sometimes the eosinophiles form 70 per cent, of the 

 total leucocytes. 



Though the evidence is in favour of the view taken 

 here that F. loa is the parental form of Mf. diurna, and 

 that Calabar swellings are due to this worm, there are 

 many points that require explanation. In some cases of 

 Calabar swelling no microfilariae have been found, though 

 repeated examinations, extending over many months, 

 have been made. In other cases where Mf. diurna is 

 common no Calabar swellings have occurred. In per- 

 sons from whom F. loa has been extracted the micro- 

 filariae have not always been found, probably because the 

 filariae were immature. 



The embryos are found in the peripheral blood in the 

 daytime, and as a rule not at night. Change of the 

 habits of the host in one case did not cause any change 

 in this periodicity. 



The living embryos are indistinguishable, except by 

 their periodicity, from those of F. bancrofti, but the 

 stained specimens can be fairly readily distinguished. 



A thorough investigation is required as to the causes 

 of the variation in the effects of this worm. Every com- 

 bination may be found : (i) Cases where Calabar swell- 

 ings, F. loa, or Mf. diurna, are found alone without 

 either of the others. (2) Cases in which F. loa have been 

 extracted, and there are Mf. diurna in the blood, but no 

 Calabar swellings. In some of these cases Calabar swell- 

 ings ultimately develop. (3) Cases in which F. loa have 



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