LIFE HISTOHY OF ASCARIS LUMBRICOIDES. 



25 



decades. The average percentage was 27.8 and the per cent by ages 

 was as follows: 



Percenlaye of ijcrxons iufcutcd with Ascaris according to age (decade of life). 



Decade of life. 



Persons 

 examined. 



Infested. 



Decade of life. 



Persons 

 examined. 



Infestcfl. 



First 



NumheT. 



9S 



3.55 



G15 



PcT cent. 

 42.9 

 33. 5 

 33.5 



Fourth 



yumher. 

 241 

 164 

 129 



P'T cent. 

 26.8 





Fifth 



25.6 



Third - . . 



Sixth and seventh 



25.6 











The frieater frequency of A.'^'aris aiiioiip; children might be ex- 

 plained in two ways : First, their habits are such that they are more 

 exposed to infection than older persons; second, children are more 

 susceptible to infection than older persons. In the case of pigs there 

 is no evident difference in the amount of exposure to infection be- 

 tween 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 gi'oups ac- 

 cording to size, small (up to 2^ inches long), medium (slender worms 

 between 2| and 5 inches long), and adult (plump worms 5 inches 

 or 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-i)iortc)ii examinations of hogs of various ages for the presence 

 of Ascaiis suuin in the intestine. 



Item. 



Hogs examined number. . 



Hogsinfosted {perce^nC 



Total worms found number. . 



Average worms per hog do 



Average worms per hog infested do 



Small worms 2 per cent. . 



Medium worms 3 do 



Adult worms •* do 



-\ge in months- 



lto2i 2Jto5 5to7 7tol2 il2tol8 18to48 



55 



19 



34.5 



82 

 1.6 

 4.5 



97.6 

 2.4 



584 

 304 

 52.1 

 1,936 

 3.3 

 6.4 

 4.2 

 49.2 

 46.5 



363 

 158 

 43.6 

 684 

 1.9 

 4.3 

 4.2 

 33.2 

 62.7 



699 



299 



42.8 



1,489 



2.1 



5 



4.2 

 35.9 

 60 



626 



238 



38 



1,243 



I 5.2 



5.6 



39.4 



54.9 



256 



91 



35. 



541 



2. 



6 



'3l! 

 67. 



.5 



All 



2,583 

 1,109 



141.1 



5,975 



12.1 



15.2 



13.1 



147.8 



149.1 



1 Weighted average or per cent. 



- Not more than 2 V inches long. 



3 Slender worms intermediate in size between small and adult worms. 



* Plump worms 5 inches or more long. 



