BUREAU OF ANIMAL INDUSTRY, 155 



serving special precautions to prevent the infection of young pigs 

 until they are at least 4 months of age, after which they are less 

 likely to become infected and less likely to suffer seriously if they 

 do become infected. As in former years, this method has proved 

 highly satisfactory in preventing losses among pigs not only from 

 worms but from other diseases which under ordinary conditions 

 destroy a large percentage of the pig crop on many farms in the 

 Corn Belt. The method is rapidly coming into use not only in 

 McLean County but in other localities, where the losses among pigs 

 in recent years, notwithstanding the effective control of hog cholera, 

 have often been so heavy that many farmers have seriously consid- 

 ered abandoning the raising of hogs. A great popular interest in 

 this method is shown by the fact that in a recent tour of the experi- 

 mental farms in McLean County, conducted by the local farm bureau, 

 between 200 and 300 persons participated, including farmers not only 

 from McLean County but from seven other counties of Illinois. 



In experiments on the effects of roundworm infestation on the 

 growth of pigs, animals that were given a single dose of roundworm 

 eggs were not apparently affected, so far as growth was concerned, 

 except during the stage of lung invasion and several weeks after- 

 wards. At the end of two months they had made normal gains. 

 Pigs subjected to repeated infections, however, were seriously af- 

 fected and at the age of 4 months weighed only about half as much 

 as other pigs of the same age and breed, kept on the same feed but 

 protected from worm infection. From another experiment evidence 

 was obtained which indicates that the invasion of the lungs by As- 

 caris larvae is a predisposing factor in lung infections with bacteria, 

 but furtlier Avork on this subject is necessary before definite conclu- 

 sions can be drawn. 



Ascaris eggs buried in the ground in Chicago, 111., in October were 

 found still alive nine months later, confirming other experiments 

 relating to the longevity of the eggs. 



TREATMENT AND CONTROL OF EXTERNAL PARASITES. 



Ox WARBLES. — Experiments in the prevention of warble infestation 

 were continued on farm cattle in the Corn Belt States and on range 

 cattle in the Southwest. Wading tanks with used automobile oil or 

 fuel oil poured on the surface of the water were used as a means 

 of applying treatment to the feet and lower parts of the legs of cat- 

 tle, which were required to pass through the tanks. Farm and dairy 

 cattle soon learnecl to pass voluntarily through the tanks, but range 

 cattle often avoided them. It was found, however, that range cattle 

 would readily pass through shallow depressions in the ground, con- 

 taining water with oil on the surface. These depressions made in 

 gateways or openings leading to watering places were used as wading 

 tanks. Gravel placed in the depressions from time to time rendered 

 the bottom hard and practically impervious. Although the oil on 

 the water in the tanks had a tendency to collect at one side during 

 windy weather, some oil usually remained near the borders on all 

 sides and animals passing through carried out more or less of the 

 oil on their feet and legs. The use of the tanks was found to reduce 

 infestation greatly but did not entirely prevent it. 



