THE DOG A3 A CABRIEB OF PARASITES AND DISEASE 



dogs — these tapeworm heads pass' uninjured to the intestine of the 

 dog and give rise to numerous very small segmented tapeworms, 

 TcBnia echvnococcus (fig. 3). The dog is practically the only carrier 

 of this tapeworm. The tapeworm attains a length of only about half 

 a centimeter (three-sixteenths of an inch) and consists of a head and 

 three segments. The sexual organs develop in the second segment 

 and eggs are present in the third segment. These eggs pass out 

 in the feces of the dog and infect pasture, soil, and water. They 

 are spread broadcast on grass, in drinking water, on products in- 

 tended for human food, on children's toys, and on all sorts of objects 

 in places frequented by the dog. The rooting habit of the hog 

 predisposes it to hydatid disease, as it is extremely likely to swal- 

 low some of these eggs in feeding if there is a 

 dog with the hydatid tapeworm anywhere around. 

 But even the most careful persons have no assur- 

 ance of safety where there are such dogs. Eggs 

 from the feces of these dogs may wash consid- 

 erable distances and ultimately land on lettuce, 

 radishes, or other vegetables. They may get on 

 the hand from contaminated tools or farm im- 

 plements, or from the dog's skin. Persons who 

 allow dogs to lick their hands or faces run the 

 risk of acquiring and ingesting the eggs of this 

 tapeworm. When such eggs, which are, of course, 

 too small to be seen with the naked eye, are in- 

 gested by man or animals, the shell digests ofl 

 and releases a small embryo armed with six hooks. 

 By means of these hooks the embryo bores its 

 way through the wall of the stomach or intestine 

 and into the blood current. Here it is swept 

 around till it lodges. At the point of lodgment 

 the embryo starts to develop into the hydatid or 

 bladder worm already noted. The parasite must always be trans- 

 mitted from the dog to other animals by the ingestion of the egg 

 from the tapeworm in the dog, and from other animals back to the 

 dog by the dog eating diseased C3.rcasses or parts of carcasses. It 

 can not be transmitted in the form of the hydatid from an infected 

 animal to another animal nor in the form of the tapeworm from one 

 dog to another. 



Prevention depends in part on a proper handling of slaughtered 

 animals and of those dying from any cause. An obvious aid in pre- 

 venting this disease would be to destroy diseased portions of animals 

 slaughtered for food or for any reason. This is best accomplished at 



Fig. 3. — EcMnococcus 

 granulosus ( Twnia 

 echinococcus) , the 

 hydatid tapeworm 

 from the intestine 

 of a dog. Enlarged 

 (after Leuckart). 



