THE DOG AS A CARRIER 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, 
Taenia eehinococcus (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 off 
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 carcasses 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. — Eehinococcus 
granulosus ( Taenia 
eehinococcus ) , the 
hydatid tapeworm 
from the intestine 
of a dog. Enlarged 
(after Leuckart). 
