LIFE HISTORY OF ASCARIS LUMBRICOIDES. 29 



young pigs are exposed, would go far toward reducing tlie losses from 

 pneumonia. 



LONGEVITY OF LARV^ OUTSIDE THE HOST. 



Stewart (lOlOa) noted tliat the newly hatched larvse eliminated 

 in the feces of rats recently fed the eggs of Ascaris lurabricoides 

 might survive for three days. He found, further, that larvse that 

 had passed througli the lungs and reached the large intestine of 

 mice if placed in tap water were alive and active at the end of two 

 hours, but were dead at the end of 24 hours. Larvas from the lungs 

 of a rabbit that died 10 days after feeding with the eggs of Asccurh 

 suum have been kept alive in physiological salt solution by the 

 writers for 13 days (Experiment No. 16). 



The survival of larvse as long as 13 days after their removal from 

 the host would seem to offer some support to Stewart's rat and 

 mouse theory, but the fact that they are so slightly resistant to un- 

 favorable conditions, such as dryness, and as observed by 'Stewart 

 may not live as long as 24 hours in tap water, is evidence very much 

 against Stewart's suggestion as to the spread of Ascaris larvse from 

 rats and mice to human beings or pigs. It is known that adults re- 

 moved from the intestine of their host can be kept alive for con- 

 siderable periods of time. For example. Hall (1917) found that they 

 may survive removal from their host as long as 26 days if kept in 

 Kronecker's solution. Many species of parasitic nematodes can 

 thus be kept alive with careful handling after removal from their 

 host. The survival of Ascaris larva? for a time if kept in phj'siolog- 

 ical salt solution after they have been removed from a host animal 

 is therefore a phenomenon not unusual among parasitic nematodes, 

 and can not be considered as indicating the probability, under natural 

 conditions, of the passage of the larvse from one host to another and 

 the resultant infection of the latter. 



NATURAL OCCURRENCE OF ASCARIS IN SHEEP. 



Sheep are occasionally found to be infested with Ascaris. Ru- 

 dolphi (1819, p. 49) mentions under the name of Ascaris ovis a 

 specimen in the collections of the Vienna Museum. Diesing ( 1851 ) and 

 von Drasche (1883) give descriptions of this specimen, and the latter 

 also describes two badly preserved specimens of Ascarf's found in 

 a sheep by Koebel. Copeman (1842) found 25 ascarids in a lamb. 

 Neumann (1884) found several specimens of Ascaris in sheep. In 

 the collections of the Bureau of Animal Industry are specimens of 

 Ascaris collected from sheep at Brookings, S. Dak., Blairsville, Pa., 

 and Bethesda, Md. Apparently in no case has a fully developed 

 female Ascaris containing well-formed eggs been found in sheep. 



