ENTOZOA. 



125 



St rongylus gigcu, male. 



to the nature of its food, which is derived from 

 the vessels of the kidney, as, where suppuration 

 has taken place around it, the worm has been 

 found of a whitish hue. 



The Round-worm (Ascaris Lwnbricoides, 

 Linn.) (Jig. 72) is the first described* and 

 most common of the Human Entozoa, and 

 is that which has been subjected to the most 

 repeated, minute, and successful anatomical 

 examinations. It is found in the intestines of 

 Man, the Hog, and the Ox. In the Human 

 subject the round worms are much more com- 

 mon in children than in adults, and are ex- 

 tremely rare in aged persons. They are most 

 obnoxious to individuals of the lymphatic tem- 

 perament, and such as use gross and indi- 

 gestible food, or who inhabit low and damp 



* It is the ix/xivc <rrfoyyv\ot of Hippocrates. 



.Fig. 72. localities. They generally occur 

 te in the small intestines. 



The body is round, elastic, with 

 a smooth shining surface, of a 

 whitish or yellowish colour ; atte- 

 nuated towards both extremities, 

 but chiefly towards the anterior 

 one (a, Jig. 72), which commences 

 abruptly by three tubercles which 

 surround the mouth, and charac- 

 terize the genus. The posterior 

 extremity (6) terminates in an ob- 

 tuse point, at the apex of which a 

 small black point may frequently 

 be observed. In the female this 

 extremity is straighter and thicker 

 than in the male, in which it is 

 terminated more acutely, and is 

 abruptly curved towards the ventral 

 side of the body. The anus is 

 situated in both sexes close to the 

 extremity of the tail, in form like 

 a transverse fissure. In the female 

 the body generally presents a con- 

 striction at the junction of the an- 

 terior with the middle third (c) in 

 which the vulva (c?) is situated. 



The body of the Ascaris lumbri- 

 coides is transversely furrowed with 

 numerous very fine striae, and is 

 marked with four longitudinal equi- 

 distant lines extending from the 

 head to the tail. These lines are 

 independent of the exterior enve- 

 lope, which simply covers them; 

 two are lateral, and are larger than 

 the others, which are dorsal and 

 ventral. The lateral lines com- 

 mence on each side the mouth, 

 but, from their extreme fineness, 

 can with difficulty be perceived; 

 they slightly enlarge as they pass 

 downwards to about one-third of 

 a line in diameter in large speci- 

 mens, and then gradually diminish 

 to the sides of the caudal extremi- 

 ty. They are occasionally of a red 

 colour, and denote the situation of 

 the principal vessels of the body. 

 The dorsal and abdominal longitu- 

 dinal lines (e, fig. 72) are less 

 marked than the preceding, and 

 by no means widen in the same 

 proportion at the middle of the 

 body. They correspond to the two 

 nervous chords, hereafter to be 

 described. 



The last species of Human En- 

 tozoon which remains to be noticed 

 is the Ascaris vermicularis (fig. 73), 

 a small worm, also noticed by Hip- 

 pocrates under the name of acrxa^?, 

 and claiming the attention of all phy- 

 sicians since his time, as one of the 

 most troublesome parasites of chil- 



lumb^i^ides dren > and occasionally of adults ; 

 in both of whom it infests the larger 



intestines, especially the rectum. 



The size of the Ascaris vermicularis varies 



