Fig. 40.—Larval Filariæ in various stage of growth from the mosquito; a to d, representing the first stage of metamorphosis during the first 36 hours, e to o, the changes occurring during the second stage, to the close of the third day; p to t, forms seen during the third stage of metamorphosis from the fourth day onwards. The figs. u, v, represent the head and tail only, whilst t shows the young Filaria in an advanced stage, and drawn to a much smaller scale, than the others which are here magnified about 125 diameters. Much reduced from Manson’s original figures.
How completely Manson took the initiative in this part of the work is evident even from Lewis’s own later observations. In a paper published in March, 1878, Dr Lewis, writing from Calcutta and speaking of the rôle of the mosquitoes, says:—“I had repeatedly examined, in a cursory fashion, these and other suctorial insects, but had not observed any parasites suggestive of these embryo-hæmatozoa, hence, when, on receipt of a communication from Dr Manson a couple of months ago, a renewed search was made, I was surprised to find that four out of eight mosquitoes, captured at random in one of the servants’ houses, harboured specimens of hæmatozoa to all appearances identical with those found in man in this country. After this, however, several days elapsed before any mosquitoes could be obtained which contained these embryo-nematoids, and the specimens obtained on the next occasion were devoid of the enveloping sheath, which appears to characterise the kind found in man out here, and apparently, according to Dr Manson, in China also.” Further on Lewis also remarks, “When the insect is caught shortly after feeding and the contents of its stomach examined microscopically, the hæmatozoa, if present, will be observed to manifest very active movements, which may possibly continue for several hours on the slide. If the insect be kept for twenty-four hours before examination it is probable that the movements of the parasites will be more sluggish, and their form probably altered owing to irregular contractions and dilatations of their substance—changes which may also occasionally be observed when embryo-hæmatozoa are preserved on a glass slide, and they may sometimes be kept alive thus, if in suitable media, for two or three days. When the insect is not examined till the third day, the contained parasites will probably manifest marked signs of disintegration—and possibly every indication of life will have disappeared from many of the specimens. After the third or fourth day I have not seen any active specimens of these entozoa in the stomach or in any part of the alimentary canal of the mosquito; those which remain have undergone more or less fatty degeneration, and are readily stained with eosin, which, as far as my experience goes, is not the case so long as they are alive and active. After the fourth or fifth day it is very rare that traces of any hæmatozoa-like objects can be detected at all, so that it must be inferred either that they have succumbed to the digestive action of the insect’s stomach or been disposed of along with the excreta.” An important addendum by Lewis records a fortunate incident as follows:—“It was observed that nearly all the mosquitoes captured in one of the servants’ houses contained hæmatozoa, so that the supply of suitable insects in all the stages of their growth became amply sufficient for all requirements. The result of the examinations under these favorable conditions has shown that although the stomach digests a great number of the ingested hæmatozoa, as mentioned above, nevertheless others actually perforate the walls of the insect’s stomach, pass out, and then undergo developmental stages in its thoracic and abdominal tissues.”
I may here observe that Sonsino has instituted a comparison between the embryos of this Filaria and those of Anchylostoma, by which it appears that the former measure 0·218 to 0·330 mm. in length, and those of Anchylostoma 0·430 mm. The hæmatozoa are about forty times longer than broad, and the larval anchylostomes only fourteen times longer. The tail of Filaria is conspicuously longer.
In the ‘Lancet’ for June 22nd, 1878, an announcement appeared from the pen of Mr D. H. Gabb, of Hastings, stating that a patient under his care formed the habitat of Filaria sanguinis hominis; and in the autumn of the same year a paper which I read to the Linnean Society in the spring was published. In that paper the following summary was offered:
1. Filaria Bancrofti is the sexually-mature state of certain microscopic worms hitherto obtained either directly or indirectly from human blood.
2. The minute hæmatozoa in question—hitherto described as Wucherer’s Filariæ, Filaria sanguinis hominis, Trichina cystica, Filariose dermathemaca, and so forth—are frequently associated with the presence of certain more or less well-marked diseases of warm climates.
3. The diseases referred to include chyluria, intertropical endemic hæmaturia, varix, elephantiasis, lymph scrotum, and lymphoid affections generally, a growth called helminthoma elastica, a cutaneous disorder called craw-craw, and also leprosy.
4. It is extremely probable that a large proportion, or at least that certain varieties of these affections are due to morbid changes exclusively resulting from the presence of Filaria Bancrofti or its progeny within the human body.