PART III.] More than One-third of the Dogs in Calcutta affected. 539 



double outline results highly suggestive of an enveloping cyst. The osmic acid 

 appears to act on the serum before causing the death of the Filaria, so that the 

 latter contracting after the serum has become partially solidified produces a clear 

 space, which may be evident at either end or alongside the worm, as may be 

 observed in the accompanying woodcut. 



It will, however, be sufficiently clear that this appearance is produced by the 

 ante-mortem contractions of the parasite, from the simple fact that the spaces are 

 nearly always along the convexities of the outline of the worm. Had the spaces been 

 due to the folds of a cyst, they would have been found along the concavities. 



Notwithstanding these minute anatomical discrepancies, which are of importance 

 in considering the natural history of the two parasites, their resemblance is 

 sufficiently striking, that I would strongly advise those who are interested in the 

 human Hsematozoon, and have not had the opportunity of examining it for themselves, 

 but are anxious to obtain a more definite conception of the Filaria sanguinis 

 \hominis than can be obtained from written descriptions and drawings, to make 

 arrangements with some of the low-caste persons employed in destroying sickly, 

 pariah dogs, to collect a few ounces of the blood of these animals. 



The fluid should be examined at first by means of a low power, such as a 

 frd of an inch objective — the layer of fluid between the slide and the covering glass 

 being as thin as possible. Should any worm-like body manifest activity on the slide, 

 the frd objective should be replaced by a good :^th or still better a ^th of an inch 

 immersion object glass. Should, however, this procedure not prove successful 

 after having tried several dogs, it will be found advisable to get the aorta itself 

 and gently scrape its lining membrane with the edge of a covering glass. Should 

 the dog be affected at all, the probability is that the parasite will be found here. 

 It must not be expected that the blood will present any peculiarity to the naked 

 eye, even though every ounce may contain thousands of em byro- worms. 



With regard to the movements of the canine variety, it may be stated that 

 they are strikingly like those of the Filaria sanguinis hominis, and not materially 

 different from the movements of Filaria-embryos generally. I have, however, frequently 

 observed the canine worms attached, at the oral extremity, to the under-surface 

 of the covering glass, or to the slide, and swinging in all directions from this fixed 

 point — the oral extremity being blunted whilst in this condition. I have watched 

 them thus attached for more than an hour, but have not observed a similar feature 

 in the movements of the human variety. 



The internal structure of both is pretty much alike; in neither is there any 

 visible differentiation of the reproductive organs, and only in a very minor degree of 

 the alimentary tract; if anything, the canine parasite is perhaps the more advanced. 



With reference to the degree of prevalence of this condition among dogs, it 

 may be stated that of the animals which I have examined in Calcutta with this 

 special object in view, more than a third were found to be affected. I have kept 



