274 PROCEEDINGS OF THE ACADEMY OF [1896. 



" filarial periodicity," as it is called, has been carefully studied by 

 Manson who found that toward sunset the embryos " begin to enter 

 the general circulation. Gradually, as the night wears on, their 

 numbers increase. About midnight they are most numerous. As 

 morning approaches they get fewer and fewer, and by 8 or 9 A. M. 

 they have disappeared." This periodicity is wonderfully adapted 

 to facilitate the escape and further development of the embryo 

 through the medium of the mosquito. Various theories of the cause 

 of " filarial periodicity " have been advanced but none of them is 

 entirely satisfactory. The most satisfactory of them is that which 

 correlates the habits of the parasite with the sleeping and waking 

 habits of the host. This, however, is simply reiterating the fact 

 without explaining it. That the approach of the embryos to the 

 surface is not entirely due to the somnolent condition (>f the host is 

 shown by the fact that it begins several hours before bedtime ; 

 while, on the other hand, the parasites begin to retire to the deeper 

 vessels hours before the usual hour of rising. It cannot be denied, 

 however, that the condition of sleep has something to do with the 

 approach of the Filaria to the surface. This is proved by a celebrated 

 experiment of Dr. Stephen Mackenzie who induced a patient who 

 harbored the Filaria nocturna to reverse his usual habits as tosleep- 

 ^ing and waking : I. e. to remain awake all night, and sleep during 

 the day. While this experiment was in progress the Filaria was 

 found in the surface vessels solely or chiefly during the day. The 

 fact that the embryos begin to find their way to the surface several 

 hours before bedtime would seem to indicate that the systemic condi- 

 tion which induces sleep is chiefly vascular and that it is of gradual 

 development. 



The refuge of the embryo o^ Filaria nocturna during the day has 

 not, as yet, been discovered. The embryos of Filaria imviitis, a 

 parasite of the dog, observe a modified periodicity and when fewest 

 in the surface vessels are found in enormous numbers in the blood 

 vessels of the lung. This is not the case with Filaria nocturna 

 for Manson has examined blood expectorated from the lungs of a 

 Filaria patient by day without finding the embryos and Myers has 

 examined blood withdrawn by aspiration from the spleen and liver 

 during the day, with negative results. 



I have elsewhere^ discussed the question of the treatment of 



1 Medical News, May 2d, 1896. 



