Stomach Worms in Sheep. 7 
larval stage, whether active at the time or in a state of suspended 
animation, continues its development, and in the course of 2 or 3 
weeks reaches maturity. 
The length of life of individual worms in the stomach has not been 
determined. Infested sheep have been kept in pens with board 
floors, which were kept clean by sweeping ana frequent scrubbing— 
the sheep being fed from raised racks and water being supplied in a 
trough which was frequently cleaned—for varying periods up to a 
maximum of 19 months, and at the end of these periods were found 
to be still infested, though the number of worms present was small. 
As the possibility of reinfection by larval worms developing from 
eggs passed in the feces of these sheep was not entirely removed, 
though greatly minimized, the results obtained do not necessarily 
indicate that the worms found at the end of the period of observation 
were all present when the experiment was begun. The experiment, 
however, while it proves nothing as to the length of life of the adult 
stomach worm, demonstrates the futility of attempting to rid sheep 
entirely of stomach worms simply by keeping them away from pas- 
ture. On the other hand, very little infection occurs among sheep 
kept in stables if cleanly conditions are maintained. Lambs have 
been kept with infested sheep in stables for long periods of time, the 
only precautions against infection being the removal of manure about 
once a week. Under such conditions they have continued in good 
health, and acquired only a very few stomach worms and other 
parasites. 
LENGTH OF TIME PASTURES MAY BE INFESTED. 
The maximum period during which the larval stomach worms are 
able to survive on pastures is not definitely known, but it has been 
found that pastures on which infested sheep had grazed were appar- 
ently still infectious after a lapse of nearly 8 months, namely, from 
October 25, when the infested sheep were removed, to June 16, when 
the pastures were tested by placing in them some lambs which had 
been raised under special precautions to avoid previous infestation. 
In cultures made September 14, 1906, from the feces of an infested 
sheep and kept thereafter in the laboratory, most of the larvz were 
dead but some were still alive, though very sluggish, on June 5, 1907, 
nearly 9 months later. Cultures in which the worms were allowed 
to develop to the final larval stage, after they were kept in cold storage 
at a temperature below freezing—in some cases as low as 12° F'.— 
still contained some living worms after 2 or 3 months, while in other 
cultures eggs and newly hatched worms not yet developed to the final 
larval stage were killed within a few hours after exposure to tempera- 
tures below freezing. 
These experiments show that pastures may remain infected for 
several months after sheep are removed from them, and that the 
