46 THOMPSON YATES LABORATORIES REPORT 
1. An irregular transverse break, at about 21 -5 per cent, of length. 
This is constant. 
2. A V-shaped spot or a transverse irregular break at a distance of about 
30 per cent, of the whole length from the anterior end. This is 
nearly always present. 
3. Represents the central aggregation of fresh specimens : an area of 
varying length in which the cells are loosely arranged — distance 
63. The point from which measurements were made was the 
middle point of this area. This is constant. 
4. An irregular sometimes oval spot, often present at distance 85. 
5. A small central bright spot, only occasional present at distance 91-5. 
We propose here, before referring to the singular feature in the life of the 
embryo filaria known as 'filarial periodicity,' to describe briefly F. diurna. 
Filaria diurna 
Manson 1 writes of this worm : — 'I have twice encountered in negroes a blood 
worm with the same dimensions and anatomical characters, so far as these have been 
made out, as F. nocturna, but differing from this latter parasite, inasmuch as it comes into 
the blood during the day and disappears from it during the night. One of these patients 
came from Old Calabar, the other from the Congo. The periodicity observed by the 
parasite was thoroughly made out by prolonged observation in one of the cases. 
As the man was in good health at the time, and was observing ordinary habits as 
regards the hours of sleeping and waking, there can be little doubt that the parasite 
was not F. nocturna. Some years previously this patient had a F. loa in one of his 
eyes ; it is just possible, therefore, that F. diurna, as I name this blood worm, is the 
embryonic form of the sexually mature F. loa. This is merely a conjecture. I have 
no further observations to support it ; indeed, the negative results as far as finding 
filariae in the blood in four cases of F. loa which I have examined, are against it. 
Nothing is known about its life history or pathological significance. From recent 
observations I believe it to be very common (1 in 4) in certain districts on the lower 
Niger, where it seems to take the place among the natives that F. perstans holds 
among the Congo negroes.' 
Our observations of a large number of cases of infection of what would be 
described as F. diurna, among natives from all parts of the west coast of Africa, 
verify the description of the blood filaria as given above by Manson. In fact, 
absolutely no difference could be detected between this embryo and that of F. nocturna, 
either in fresh or in stained specimens. In stained specimens the characters and 
positions of the spots resemble closely those of F. nocturna. 
1. Manson, Tropical Diseases. London, 1900. P. 532. 
