LIFE HISTORY OF ASCARIS LUMBRICOIDES. 73 
the air sacs being almost entirely filled in with the serosanguineous 
exudate. Extensive immigration of leucocytes and round-cell in- 
filtration characteristic of acute inflammation are well marked. In 
other portions of the section the alveoli are enlarged, indicating a 
compensatory emphysema. Similar appearances are shown in figure 
6, a photomicrograph of a portion of the lung of a pig one week after 
the ingestion of Ascaris suum eggs. 
Fic. 6.—Ascaris suum. lLarve in cross section in portion of lung of pig 1 week after 
infection. Photomicrograph. Highly magnified. 
DEATH OF MIGRATING LARVZ. 
It is a general rule among animals that in species in which large 
numbers of young are produced the chances are slight that any 
given individual will reach maturity. In the case of Ascaris, which 
produces eggs in enormous numbers, there is a great loss of -life 
among the parasites not only in the death of the eggs that do not 
reach a suitable host, but also in the failure of some eggs to hatch 
after they are swallowed, in the prompt elimination of such eggs 
and many newly hatched larvee in the feces, and in the death of 
some of the larve in the course of their migrations through the body. 
Finally a further loss occurs in the elimination of larvee in the feces 
after they have returned to the intestine following their migrations 
through the lungs. There is thus a great waste of life all along the 
