ROUND-WORM 



659 



or ova are very small, being only about 4^7 inch in length, and can 

 be seen only under a powerful lens or with the aid of a microscope. 



When the eggs reach the ground they become mixed with earth 

 and water, and these contaminated substances, especially the water, 

 are taken into the stomach of the growing animals. The stomach 

 juices set the young parasite free from the shell of the egg, and the 

 newly hatched worm passes into the bowel, where it rapidly devel- 

 ops into a full-grown parasite. Young pigs and growing shoats are 

 especially susceptible to these 

 round-worms, and may show 

 very marked symptoms as a re- 

 sult of infestation by them. 



Predisposing influences in the 

 production of round-worm infes- 

 tation are those which tend to 

 allow drinking of contaminated 

 water and eating of dirty food 

 soiled with mud or earth con- 

 taining these eggs. Eating off 

 of dirty feeding floors and drink- 

 ing of water from shallow ponds 

 and dirty watering troughs are 

 especially prominent factors in 

 encouraging the development of 

 this disease among young ani- 

 mals. If the pig be unthrifty 

 from any cause, such as diges- 

 tive trouble, chronic cough, or 

 any other exhausting disease, 



the chances for development of round-worm infestation are the 

 more marked. Strong, healthy pigs may be able to throw off the 

 parasites without developing any signs of being wormy. 



Symptoms. — Round-worms do not produce any typical chain 

 of symptoms that would enable one to make an absolute diagnosis 

 of the condition present unless they were to find the worms in the 

 discharges from the bowels. There are, however, a certain group 

 of symptoms found in worm-infested animals that may lead to a 

 quite convincing suspicion that worms are present. 



Fig. 91. — Ascaris suis (a young 

 one): a, Head extremity; b, tail 

 extremity. (From Kaupp's Animal 

 Parasites.) 



