24 BULLETIIT 811, TJ. S. DEPT. OF AGKICULTUEE. 



line in the development of Ascaris that is offset only by the abundant 

 fertility of the parasite. 



We have repeatedly made observations showing that Ascaris 

 larvae may die in the course of their migrations through the body. 

 That larvse die in the liver is evident from the finding of dead and 

 degenerated larvae in the liver of a mouse which was killed 296 

 days after it had been fed Ascaris suuom eggs. There was a small 

 encapsulated tumor near the margin of the liver, containing a caseous 

 matei-ial and several dead and degenerated Ascaris larvse. On sev- 

 eral occasions dead and more or less degenerated larvae have been 

 found in the lungs, for example in a rabbit 86 days after infection 

 and in a pig 65 days after infection. It is quite probable that the 

 larvae^ that migrate to the spleen, thyroid, and other organs outside 

 the usual path of migration ultimately die and become encysted and 

 absorbed or perhaps in some cases stimulate the surrounding tissues 

 to other reactions. In this connection the observations made by Gay- 

 lord and Marsh (1914) are of interest. It was observed that dogs 

 fed on sediment from fishponds developed a thyroid hyperplasia 

 and that in the thyroids of such animals there were sometimes found 

 larval nematodes {Agamonematoduin, gaylordi Hansom). It ap- 

 pears quite possible that these larvae were the young of some nematode 

 occurring in the fish, and that ingested by the dogs they underwent 

 migrations somewhat similar to those of Ascaris larvae, some of them 

 finally coming to rest in the thyroid. The etiological relation of 

 these nematodes to the hyperplastic growths of the thyroid observed 

 by Gaylord and Marsh is problematic. A somewhat similar associa- 

 tion of dead nematode larvae and other parasites with various sorts 

 of neoplasms has been noted by different observers. No evidence has 

 yet been obtained that the death of migrating Ascmis larvae in the 

 tissues of the host is followed by any serious consequences. 



RELATION OF AGE TO ASCARIS INFESTATION. 



It is a well-known fact that among human beings children are 

 more commonly infested with Ascaris than adults. This difference is 

 perhaps most noticeable in localities where the parasite is compara- 

 tively rare. In other places, where a large percentage of the popu- 

 lation are carriers of Ascaris the fact that the parasite is of more 

 frequent occurrence among children is less striking, but nevertheless 

 unless practically the entire population harbor the parasites there is 

 a more or less distinctly greater frequency in infestation among the 

 younger individuals than among the older. For example, in the 

 Philippines, Garcia (1917) from fecal examinations of 1,603 persons 

 of various ages found the highest percentage of infestation among 

 persons in the first decade of life, less among those in the second and 

 third decades, and still less among those in the fourth to seventh 



