82 



DISEASES OF THE DIGESTIVE APPARATUS 



INTESTINAL PARASITES. 



(Hehninthiasis.) 



Round Worms, Maw Worms (Ascaris Mystax). 



Natural History. — The round worm of the dog, ascaris mystax, 

 ascaris marginata, is Avhite or yellowish-white, slightly reddish in color 

 and twisted in spirals; there is a difference in the two sexes (see Fig. 

 40), the males are about 6 cm. and the female about 12 cm. Their 

 thickness varies from 1 to 1.5 mm. The head is slightly flattened and 

 fitted with two wing-shaped borders, which start from the mouth and 

 enlarge slightly as they pass posteriorly. The mouth is a round small 

 opening, and fitted with three to six small lips, which cover a number of 

 proportionately large teeth. The caudal end of the male parasite is 



n o 



Fig. 40. — Ascaris mystax. 



curved and pointed and has numerous small papillae on each side. The 

 caudal end of the female is pointed and straight. The vulva is about the 

 end of the first fourth of the body from the head. In the genital organs 

 there can generally be seen quantities of round eggs that on examination 

 are found to have a thick, hard shell, which is marked by numerous 

 small grooves. These eggs are found in enormous quantities in the 

 fa*ces of all dogs affected with the round worm (see Fig. 15). The de- 

 velopment of the embryo is not yet thoroughly understood, but from the 

 experiments of Grassi, Penberthy, Albrecht, Frohncr, it has been dem- 

 onstrated that the intestines of puppies that have never taken any- 

 thing but the mother's milk, contain numerous ascarides, and they have 

 demonstrated that an intermediate host is not necessary, but the worms can 

 be developed directly from the eggs in another animal of the same species. 

 As a rule, the round worms cause little trouble in the dog. Pem- 

 bcrthy found 250 in a six weeks old puppy that had constant vomiting, 



