Oe et ee 
Py er es, 
i lt 
LIFE HISTORY OF ASCARIS LUMBRICOIDES. _ 25 
decades. The average percentage was 27.8 and the per cent by ages 
was as follows: 
Percentage of persons infested with Ascaris according to age (decade of life). 
Persons 
Decade of life. teens Infested. Decade of life. patel: Infestee. 
Number. | Per cent. ; ‘| Number. | Per cent. 
IBiRSt ee pease cee 98 AOI OVA ISOs nyoee Soceneacdagessc 241 26. 8- 
Second eee eeaise eee aeciss Se 355 exe oad Wed U6 ees eerie ese ah hm 164 : 25.6 
Di sees ee ee See ee ae 615 33.5 || Sixth and seventh-..-.----.-- 129 25. 6-55 
The greater frequency of Ascaris among children might be ex- _ 
plained in two ways: First, their habits are such that they are more. 
exposed to infection than alee persons; second, children are more. 
susceptible to infection than older persons. In ‘ihe case of pigs there 
is no evident difference in the amount of exposure to infection be- 
{ween young and old animals except that the older pigs during their __ 
lifetime have had greater opportunities of becoming infected than 
younger pigs because they have lived longer, so that if equally sus=_ 
ceptible at all ages older pigs should be more commonly and more -. 
heavily infested than younger pigs. As a matter of fact, however, 
there is a greater frequency of infestation among young than among 
old pigs, and they harbor more parasites than the older animals, 
so that it appears that young animals are more susceptible than 
older ones. The following table is based upon a post-mortem 
examination of the intestines of 2,583 hogs of various ages slaugh- 
tered for market at Chicago abattoirs. The examinations were made 
and the ages of the animals estimated by Dr. H. B. Raffensperger. 
Dr. Raffensperger sorted the worms found into three groups ac- 
cording to size, small (up to 23 inches long), medium (slender worms 
between 24 and 5 inches long), and adult (plump worms 5 inches 
cr more long). Great care was taken in examining the contents of 
the intestine to obtain every worm possible, but it is quite certain 
that some of the small worms were overlooked, so that the figures 
are less accurate for the small than for the medium and adult worms. 
Results of post-mortem examinations of hogs of various ages for the presence 
of Ascaris suum in the intestine. 
Age in months— 
Item. | All 
1to2} |2ito5 | 5to7 |7to12 |12to018| 18t048 
ages. 
Hogs examined 2 922-25 js assaenin = porn eR: 2 55 ae 363 a 636 256 2, 583 
F See Os |r ik 158 99 38 91 1,109 
EUS MEGS Sco so cegagsoaeces 2oeu0e {percent..| 34.5] 52.1] 43.6] 42.8| 38 35.5 | 141.1. 
Total worms found -.:.-.:-.22.5.2-- number..| 82 /|1,936 684 1,489 (1,243 541 5, 975 
Average worms per hog. ...-...-.-.---- CloReac 1.6 3.3 1.9 2.1 2 2-1 12.1 
Average worms per Hae infested....---- do...- 4.5 6.4 4.3 > 5.2 6 15.2 
Small Worms 2525. same tects oe per cent..|..-..--- 4.2 4.2 4.2 5.6 8 13.1 
Mediumiwortis! 42523 2asoe2- 2 2 eee dove 97.6 49.2 33.2 35.9 39.4 31.4 1 47.8 
AGult WOrm's Sooo. sen ceeaceetaeise dome 2.4 46.5 62.7 60 — |. 8429 67.8 149.1 
1 Weighted average or per cent." 
2 Not more than 2} inches long. 
3 Slender worms intermediate in size between small and adult worms. 
4 Plump worms 5 inches or more long. 
