24 BULLETIN 817, U. S. DEPT. OF AGRICULTURE. 
line in the development of Ascavis that is offset only by the abundant 
fertility of the parasite. | 
We have repeatedly made observations showing that Ascaris 
larvee may die in the course of their migrations through the body. 
That-larvee die in the liver is evident from the finding of dead and 
degenerated larve in the liver of a mouse which was killed 296 
days after it had been fed Ascaris suwm eggs. There was a small 
encapsulated tumor near the margin of the liver, containing a caseous 
material and several dead and degenerated Ascaris larve. On sevy- 
eral occasions dead and more or less degenerated larve 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 
larve, 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 (Agamonematodum gaylordi Ransom). It ap- 
pears quite possible that these larvee 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 larve, 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 larve 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 Ascaris larve 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. stil] less among those in the fourth to seventh 
