LOA WORM 



309 



tissue in and about the eyes, but may also be found creeping 

 under the skin of fingers, breast, back, etc. A loa is said to travel 

 at the rate of about an inch in two minutes, and to become 

 especially active in the presence of direct warmth on the skin, 

 as before a fire. The migration of the worms causes itching and 

 a " creeping " sensation, and in some unexplained way gives rise 

 to temporary swelhngs, from half an inch to four inches in diame- 

 ter, known locally as " Calabar swellings." These swelhngs 

 may shift their position an inch or more a day, and may disap- 

 pear to reappear somewhere else. This relation of Loa to Cala- 

 bar swellings has not been definitely proved but there is strong 

 evidence for it. In one case Manson succeeded in finding 

 great numbers of microfilariae of Loa in lymph taken from one 

 of these swellings, a fact which gives color to Manson's hypothe- 

 sis that the swellings might be due to the emission of larvae from 

 the parent worm into the connective tissue. The larvae of the 

 parasite (Fig. 124C), very closely resembling the microfilariae 

 of F. bancrofti, occur in the blood in great numbers, but they 

 have a periodicity di- 





A 



B 



rectly opposite to that 

 of the latter species in 

 that they swarm in the 

 peripheral blood in the 

 daytime and withdraw 

 to the larger vessels at 

 night. The living 

 larvae of the two species 

 cannot readily be dis- 

 tinguished from each 

 other in fresh blood, 



u 4- ■ J ■ J ^ + ■ rl ^^"^^ ^^^' Comparison of killed and stained speci- 



but m dried and stained ^^^^ ^f Microfilaria bancrofti and mf. loa. A, mf. 



preparations the dead 6ancro/(i, — note graceful curves; B,m/.ioa, — note 



• 1 1 irregular scrawl-like curves; C, tails of m/. loa; D, 



organisms can easily be ^aUs of mf. bancrofti. (After Manson.) 



identified. The micro- 



filarice bancrofti are found lying in smooth graceful curves (Fig. 

 129A), while the microfilarice loa die in ungraceful and irregular 

 scrawl-like positions (Fig. 129B), with the tail nearly always 

 sharply turned back (Fig. 129C). 



There is much evidence that the intermediate hosts of L. loa 

 are mangrove flies of the genus Chrysops, which belong to the 



