A Description of the Thread-worm, Filaria immitis. 163 



gencies in size, the only marked difference is the " delicate envelop- 

 ing tube." As before said, though observed in the human worm 

 during life, it was not constant after death, a feature clearly- 

 pointed out by Dr. Lewis ; it received considerable modifications 

 on the passing of the worms from life to death, and competent 

 observers failed to detect it in a few preserved specimens sent to 

 Netley. On the other hand, in the majority of the dead young 

 canine worms there wore no indications of its presence, although a 

 halo of light thrown from the curved sides of the worm's body gave 

 a phantom existence to it ; as before remarked, also, the aspect of 

 the tail end of the male at first strongly suggested it ; yet in a few 

 instances, especially after the staining of the textures by magenta, 

 a faint outline could be traced along the worm for some distance 

 which was not dissipated by focal alteration or varying the direc- 

 tion of the source of illumination of the microscope. Whether this 

 unquestionable delicate line, locally bulging out occasionally, was 

 due to the presence of an " enveloping tube," or a mere separation 

 of the epidermis en masse from the cutis, I cannot state with 

 certainty; the examination of the living young canine worm is 

 necessary to determine the point ; but meanwhile, the doubt 

 thrown on its existence in the dead canine cannot, in the face 

 of the death modifications observed in the delicate tube of the 

 human, be considered as sufficient to differentiate the one worm 

 from the other. That the human blood worm is the young brood 

 of a filaria closely allied specifically to the filaria of the dog can hardly 

 be a subject of controversy ; the only point of doubt is the question 

 of identity, and certainly the grounds for assuming it are strong. 



Concerning the life history of the canine worm, it appears to me 

 that the specimens, the subject-matter of this paper, tend to set one 

 part of it at least at rest. It is quite clear that the mature worm can 

 infect its host, and it seems equally deducible that the young may 

 develop into mature helminths in the dog's blood-vessels. In this 

 example we have mature males, females brood-containing, and a free 

 young brood varying greatly in size and suggesting growth, in the 

 same host. Whence and how came the mature worms ? Considering 

 their size and the absence of any boring apparatus as a means of 

 locomotion through the tissues, we may put on one side the idea of 

 their reaching the vascular canals in a mature state ; the worm also 

 is viviparous, and the question of the conveyance of soft, frangible, 

 immature ova may be disposed of ; the free active young remain. 

 The faculty of migration of the white corpuscle of the blood through 

 the tissues of the body has been demonstrated ; the diameter of the 

 body of the young filaria is considerably below that of the corpuscle ; 

 hence with the brisk, wriggling, movements of life, the possibility 

 of their passage through a mucous membrane, especially through 

 the soft granulations of an ulcer, is quite within the bounds of 

 reality. Based upon the facts we know, we may in imagination 



