Mikrofilariæ | Mikrofilariæ | ||||
| Lungs | 134,821† | Spleen | 1,666 | ||
| Liver | 4,884 | Brain | 3,833 | ||
| Kidneys | 15,253 | Glands | 0 | ||
 | Glomeruli | 8,008 | Marrow | 0 | |
| Parenchyma | 7,245 | Blood | 3,000 | ||
† These figures refer to 1 c.c. of each organ, and were estimated by cutting sections of definite thickness (30 µ to 40 µ) and counting the filariæ in a definite area of section, e.g., 1/4 cm.2 The organs before removal from the body have their vessels tied, and are then fixed in hot alcohol.
The following data of Rodenwaldt refer to the larvæ of Filaria immitis in the dog. They are commoner in organs than in vessels, and especially in the capillaries of the organs, but in the lungs they appear to be equally distributed in capillaries, arteries and veins.
The length of life of larvæ is unknown, but they appear to be destroyed in the kidneys, as dead calcified specimens are fairly numerous in the capillaries of the vasa recta of the medullary substance.
Kidneys: mainly in the glomerular capillaries and those of the vasa recta.
Liver: in the capillaries of the portal system, especially in those between the interlobular and the central intralobular veins.
Periodicity of Larvæ.[302]—Roughly speaking, the larvæ of Filaria bancrofti are found in the peripheral blood only during the night, disappearing (but not entirely) during the daytime. Their periodicity and that of Loa loa larvæ is shown by the table on p. [394], based on that of Smith and Rivas (Amer. Journ. Trop. Dis. and Prev. Med., 1914, vol. iii, p. 361).
It was discovered by Mackenzie that this periodicity could be reversed by making the patient sleep during the daytime, showing that the phenomenon was in some way dependent on sleep or its attendant phenomena. Rodenwaldt gives the following explanation of the phenomenon of periodicity:—
Mikrofilariæ come to rest in capillaries. After passing up the thoracic duct they would reach the capillaries of the lungs by the superior vena cava. Here they occur in immense numbers. In the case of Loa loa larvæ (which have a diurnal periodicity) some of these are forced out by the increased force and rapidity of the pulmonary circulation during the day, but are able to rest (owing to their sticky sheath?) in the peripheral capillaries on their way to the capillaries of the organs. During the night the force of the current through the lungs is relaxed and consequently they are able to remain in the pulmonary capillaries and do not appear in the capillaries of the systemic circulation. If it is true that the periodicity of Loa loa cannot be reversed by changing the hours of sleep, then the explanation is incomplete. In the case of the larvæ of Filaria bancrofti (which have a nocturnal periodicity), in order to apply the same explanation we must further assume that the mikrofilariæ have less power of resisting the force of the capillary current (i.e., are less sticky). They are washed out of the pulmonary capillaries by day and by night, but it is only at night, when the blood stream in systemic capillaries is less rapid, that they are able to rest there. In the daytime they are washed on until they reach the capillaries of the organs (possibly again the lungs). The reversal of the periodicity by sleeping during the daytime admits of a similar explanation. If this explanation be true, then a prolongation of the day conditions, e.g., by continued exercise, should result in still keeping the larvæ out of the circulation, but this does not appear to be the case.
Larvæ of L. | Average 132. | Case 1. | Average 1,000 | Case 2. | Average 1,570 | ||
2 | a.m. | 9 | – 123 | 3,500 | + 2,500 | 6,500 | + 3,930 |
4 | a.m. | 11 | – 121 | 3,200 | + 2,200 | 5,200 | + 3,630 |
6 | a.m. | 41 | – 91 | 2,800 | + 1,800 | 2,000 | + 430 |
8 | a.m. | 168 | + 36 | 900 | – 100 | 1,100 | – 470 |
10 | a.m. | 298 | + 166 | 210 | – 790 | 350 | – 1,220 |
12 | noon | 531 | + 389 | 30 | – 970 | 50 | – 1,520 |
2 | p.m. | 252 | + 120 | 20 | – 980 | 40 | – 1,530 |
4 | p.m. | 146 | + 14 | 10 | – 990 | 30 | – 1,540 |
6 | p.m. | 91 | – 41 | 40 | – 960 | 40 | – 1,530 |
8 | p.m. | 23 | – 99 | 60 | – 940 | 100 | – 1,470 |
10 | p.m. | 5 | – 127 | 600 | – 400 | 800 | – 770 |
| 12 | midnight | 5 | – 127 | 750 | – 250 | 2,600 | + 1,030 |
Total | 1,580 | — | 12,120 | — | 18,810 | — | |