LIFE HISTORY OF ASCARIS LUMBRICOIDES. 15 



that the hirvaj of Ancarin migrate actively throu<ih the tissues to the 

 lungs after hatching in the intestine, and he considers that the pos- 

 sible carriage of the larvae in the circulation, if it does occur at all, 

 is of secondary importance. He would also explain the presence of 

 larvae in the spleen, kidneys, and various other locations in which he 

 has found them in addition to the lungs and liver, as resulting from 

 an active penetration of the larvae through the tissues unaided by the 

 circulation. 



DEVELOPMENT IN THE INTESTINE. 



After reaching the small intestine following their migration 

 through the lungs, Ascaris larva?, if in a suitable host, settle down and 

 develop to maturity. It appears, however, that some of them may 

 pass on out of the intestine and perish, just as they do in the case 

 of rats, mice, guinea pigs, and rabbits. Stewart (1918b) noted dead 

 Ascaris larvae in the feces of a pig 11 days after feeding the eggs. 

 Accordingly, even though the host is one in which the parasites can 

 reach maturity, not every larva that succeeds in completing the 

 cycle through the lungs is able to establish itself in the intestine. 

 This would seem to be the probable explanation of the fact that 

 pigs fed the eggs of Ascaris suum experimentally and afterwards 

 showing evidence of lung invasion by the larvae, may, when killed 

 after a lapse of time sufficient for the development of the parasites 

 to maturity or to a stage approaching maturity in the intestine, be 

 found to hai'bor only a few worms or' none at all. Such failures 

 have been noted by us. For example, a pig 27 days old was fed 

 numerous eggs of Ascaris siiawi, October 4, 1917. Another lot of 

 eggs was fed to this pig November 10. On November 17, or 44 days 

 after the first feeding and 7 days after the second, the pig was killed. 

 The liA'er and lungs shoAved nimierous petechiae similar to those 

 occurring in other experiment animals in association with the in- 

 Aiision of these organs by Ascaris larvae, but no larvae were seen in 

 the preparations examined. In the small intestine there were 8 

 immature Ascaris^ 5 of which were measured and found to rang© 

 from 60 to 88 nnii. in length. Another pig, from the same 

 litter, that was fed Ascaris suum eggs September 22, when 15 days 

 old, died 7 days later and showed numerous larvae in the lungs, 

 trachea, and pharjaix, those in the trachea ranging in length from 

 0.67 to 1.33 mm. (Experiment No. 19). 



It is quite likely that the worms found in the intestine of the first 

 pig came from the eggs fed 44 days before, but the result of the 

 experiment by itself can not, of course, be considered conclusive 

 proof that development of Ascaris in the intestines of pigs follows 

 the ingestion of the Qg,g®, nor that the larvae wdiich mature in the 

 intestine first migrate to the lungs and back again before they settle 



