208 FILARIA BANCROFTI [CH. 



rarely seen in the blood of a patient, or, if present, only in very 

 small numbers, but as evening approaches about five or six 

 o'clock the filariae begin to enter, the peripheral circulation in 

 gradually increasing numbers. The maximum is usually 

 attained about midnight, when it is no uncommon thing to 

 find 300, or even 600, in every drop of blood. The numbers 

 then begin to diminish, and by eight or nine o'clock in the 

 morning the filariae have disappeared again for the day. This 

 diurnal periodicity may be maintained with regularity for 

 years. Manson was able to shew that during the daytime the 

 parasites retire to the lungs, heart and larger arteries, where 

 they may be found in enormous numbers. In the case of a 

 filarious patient who had committed suicide during the daytime, 

 the parasites were found to occur in the various organs in the 

 following numbers, which indicate the average per slide : 

 liver, I ; spleen, i ; brachial venae comites, 28 ; bone marrow, o ; 

 muscle of heart, 122 ; carotid artery, 612 ; lung, 675. In the 

 lungs the filariae were found lying outstretched or coiled in 

 the blood-vessels, both small and large. In the carotid they 

 occurred in enormous numbers on its inner surface, though 

 how they managed to maintain their position in the blood 

 current remains unexplained. 



Many authors have attempted to explain this remarkable 

 periodicity in the occurrence of the parasites in the peripheral 

 circulation. Mackenzie shewed that it was in some way con- 

 nected with sleep, for by reversing the usual habits, and 

 making a patient sleep during the day and work at night, it 

 was found that, after a few days of hesitation, the filariae 

 became diurnal instead of nocturnal. These results have also 

 been confirmed by Annett, Button and ElUott working in 

 Nigeria. Carter supposed that the embryos were carried into 

 the circulation at the end of each day by the overflowing of 

 chyle that follows alimentation. Myers suggested that the 

 embryos are only laid at night and all die before the morning. 

 Scheube supposed that the passage of the embryos from the 

 lymphatics into the blood was prevented during the day by 

 muscular work and digestion, and facilitated at night by the 

 relaxation of the muscles. Von Linstow explained it on the 



