ASCARIDJE 231 



Ascaris larvae in rats and mice, the various contributions of other in- 

 vestigators toward the solution of the problem of the life history of 

 Ascaris lumbricoides and related parasites, and our own experiences, 

 appear to justify certain conclusions, some of which in anticipation of a 

 more extended statement in a future paper, may be briefly given as 

 follows: 



"The development of Ascaris lumbricoides and closely related forms 

 is dii'ect, and no intermediate host is required. 



"The eggs, when swallowed, hatch out in the alimentary tract; 

 the embryos, however, do not at once settle down in the intestine, but 

 migrate to various other organs, including the liver, spleen, and lungs. 



"Within a week, in the case of the pig Ascaris, the migrating larvae 

 may be found in the lungs and have meanwhile undergone considerable 

 development and growth. 



"From the lungs the larvae migrate up the trachea and into the 

 esophagus by way of the pharynx, and this migration up the trachea 

 may already become established in pigs, as well as in artificially infected 

 rats and mice, as early as a week after infection. 



"Upon reaching the ahmentary tract a second time after their passage 

 through the lungs, the larvae, if in a suitable host, presumably settle 

 down in the intestine and complete their development to maturity; 

 if in an unsuitable host, such as rats and mice, they soon pass out of 

 the body in the feces. 



"Heavy invasions of the lungs by the larvae of Ascaris produce a 

 serious pnevunonia which is frequently fatal in rats and mice and ap- 

 parently caused the death of a young pig one week after it had been 

 fed with numerous Ascarid eggs. 



"It is not improbable that ascarids are frequently responsible for 

 lung troubles in children, pigs, and other young animals. The fact 

 that the larvae invade the lungs as well as other organs beyond the 

 alimentary tract and can cause a serious or even fatal pnemnonia in- 

 dicates that these parasites are endowed with greater capacity for harm 

 than has heretofore been supposed. 



"Age is a highly important factor in determining susceptibility to 

 infection with Ascaris, and susceptibility to infection greatly decreases 

 as the host animal becomes older. This, of course, is in harmony with 

 the well-known fact that it is particularly children and young pigs 

 among which infestation with Ascaris is common, and that Ascaris is 

 relatively of rare occurrence in adult human beings and in old hogs." 



ASCARIASIS 



Ascariasis occurs most frequently in young animals, those matured 

 rarely harboring the worms in such numbers as to bring about symptoms 



