26 BULLETIlsr 817, U. S. DEPT. OF AGRICULTURE. 



From the table it appears that the highest percentage of intes- 

 tinal infestation with Ascaris is found in pigs between the ages of 

 2^ and 5 months, about half of which are infested. Beyond this age 

 ,the percentage of infestation gradually decreases until among old 

 hogs over 1^ years of age only about one in three is infested. 



The figures relating to the numbers of worms of different sizes 

 found are of interest with reference to the question of the age at 

 which pigs are most susceptible to infection. We know that about 

 2^ months is required for Ascaris to reach maturity after the eggs 

 have been ingested. We should therefore expect few if any adult 

 worms among the pigs of the first age class (1 to 2^ months), and 

 this is the case, less than 3 per cent of the worms present in these 

 young pigs being adult worms. In pigs 2^ to 5 months old on the 

 other hand nearly one-half of the worms are mature, in pigs of the 

 next class (5 to 7 months) nearly two-thirds of the worms are ma- 

 ture, then there is a slight decrease in the proportion of mature 

 worms in the next two age groups, the proportion again increasing 

 in pigs 1^ to 4 years old in which oyer two-thirds of the worms are 

 mature. 



It is not known how long an individual Ascaris may live, but in 

 view of the rather large size of the worm and its slow growth to 

 maturity it is probable that it is long-lived ; quite likely it may live 

 a year and perhaps much longer. Thus, infested pigs a year or more 

 old may as a rule have acquired their worms while still very young, 

 no additional infection having occurred after the first few months 

 of life. The table, however, shows that pigs continue to be suscep- 

 tible to infection as they grow older. In fact, the percentage of 

 small worms among pigs 12 to 18 months old is higher than among 

 the pigs of the younger groups and even among the oldest pigs {1^ 

 to 4 years old) small worms were occasionally encountered, indicat- 

 ing recent infection, a considerable number (nearly one-third) of the 

 worms present being of medium size, indicating comparatively recent 

 infection (probably within 2^ months). The table nevertheless 

 seems to show that pigs less than 5 months old are considerably more 

 susceptible to infection than older pigs. 



Without attempting further analysis of the figures given in the 

 table, we may conclude that among the pigs coming to the Chicago 

 market slightly more than half of those less than 5 months old have 

 been found to be infested with Ascaris^ and that among older pigs 

 the frequency of infestation progressively decreased with age until 

 among pigs 1| years or more old only about one animal in three was 

 infested. Further, the pigs less than 5 months old showed a greater 

 average number of worms than older pigs, although as a natural 

 result of the slow growth of the parasites they showed relatively 

 fewer adult worms. Finally, it may be concluded that young pigs are 



