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



tinction between the parietes and the inner mass was no less apparent 

 than when the body continuity was preserved, but no differentiation 

 of the inner mass into organs was determinable. In Plate XXXII., 

 Fig. 17, an entire worm, highly magnified, has been drawn by the 

 camera lucida, while, for comparison, a red and white blood corpuscle 

 lying under the same microscope slide have been outlined on the 

 same Plate (Fig. 18). The average length of embiyos within the 

 body of the mother was y^o inch by osVo inch breadth, but a con- 

 siderable latitude in size was observed and a proportionate thickness 

 to length, varying from 1 to 16 to 1 to 28 ; hence, as compared with 

 these, the fi'ee young worm was longer and narrower, the thickness 

 of the body more uniform, there was less of the transparency of 

 the tail end, more clear foreshadowing of internal organs and body 

 striation, more rounded outhne of the anterior end of the worm. 

 Among the free young, moreover, while retaining the relative pro- 

 portion of length to breadth, there were some as small as x^o inch 

 long, while a few were as large as -V inch, clearly suggesting growth 

 since birth. Another feature was conspicuous as regards the tail 

 end — a division of the young into two categories, the one with the 

 posterior extremity of the worm tapering off cyKndrically into a 

 point, the other with this portion flattened from side to side, or 

 from above downwards, and spirally twisted, apparently distinguish- 

 ing even at this early stage the female from the male. In this 

 flattened spirillum the aspect of the worm at first sight strongly 

 suggested the existence of an enveloping membrane to the tail end, 

 similar to that observed in the human filaria during life. 



From these remarks it will be seen that the microscopic young 

 worm clearly and accurately foreshadowed the mature animal. 



General Observations. — In the ' Veterinarian,' Jan. 1873, the 

 editor asserts that " nematodes are common enough in the blood- 

 vessels of the young ass, colt, and some other animals." MM. 

 Grube and Delafond originally detected minute worms in the canine 

 blood, about y^ inch in length, and " less than a blood corpuscle in 

 diameter." They found them in the vessels in all localities, but 

 none in the lymph, chyle, secretions, and excreta. Injected into 

 the blood of a non- contaminated dog they were traceable at the end 

 of three years ; they hved 89 days when transferred to the blood of 

 two rabbits, but died when placed in the serous and cellular tissues 

 of dogs ; it was clear that their habitat was the blood. On one 

 occasion naked-eye worms, supposed to be the parent worms of the 

 microscopic forms, were found lodged in a clot in the right ventricle 

 of the heart, 4 females, 2 males, from 5 to 7 inches in length, and from 

 ^1^ to yV inch in diameter, and to these they gave the name of Filaria 

 papulosa hmmatica canis domestici. This instance of mature 

 worms, coexistent with the microscopic animals, was noted but once 

 in 29 aflected dogs : the ascribed parentage is apparently doubted 



