LIFE HISTORY OF ASCARIS LUMBRICOIDES. 23 



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 AscaHs siium eggs. 



Fig. 6. — Ascarts suum. Larva? in cross section in portion of lung of pig 1 week aftei 

 infection. Photomicrograph. Highly magnified. 



DEATH OF MIGRATING LARV^. 



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 Ascans, which 

 produces eggs in enormous numbers, there is a great loss of life 

 among the parasites not only in the death Q.f 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 larvse in the feces, and in the death of 

 some of the larvae in the course of their migi-ations through the body. 

 Finally a further loss occurs in the elimination of larvte 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 



