BUREAU OF ANIMAL INDUSTRY. 127 



later. A careful study has also been made of the method for deter- 

 mining nitrates in meats. The conventional methods were found un- 

 suitable for work which requires a high degree of accuracy. Pre- 

 liminary work with the nitron method has given promising results. 



ZOOLOGICAL DIVISION. 



B. H. Ransom, Chief. 



ROUNDWORMS OF SHEEP. 



At the bureau farm (leased) near Vienna, Va., approximately 100 

 ewes and lambs were used in the experiments of 1915 with reference 

 to parasitic roundworms. These animals were separated into four 

 lots. Lot A (ewes and lambs) was kept continuously on the same 

 pasture from May to September. Lot B (ewes and lambs) was kept 

 on a double pasture from May to September, grazing alternately two 

 weeks in each of the two parts. The ewes and the lambs of Lot C 

 were kept separate except at noontime and at night, when they 

 were allowed together in a barn with slat floors, which were fre- 

 quently cleaned and disinfected (at least once a week). During 

 the day the lambs were allowed to graze on temporary pastures, and 

 it was planned to move them once a week to fresh ground, but owing 

 to certain circumstances this plan was not followed strictly. During 

 the latter part of the summer they were moved week by week over the 

 same areas grazed during the early summer, a new crop meanwhile 

 having been planted and grown. Lot D (ewes and lambs) from 

 May to September were moved once a week to fresh pasture, and 

 were kept together most of the time, the ewes occasionally being 

 separated from the lambs and grazed on infested pasture when the 

 available fresh pasture was limited. 



Lambs from each of the lots were killed and examined in Septem- 

 ber or later, at least five from each lot being examined. Those which 

 died at any time during the progress of the experiments also were 

 examined. Eleven were examined from Lot A, 18 from Lot B, 5 

 from Lot C, and 12 from Lot D. 



No material difference was observed in the degree of stomach- worm 

 infestation in the various lots, but it is noteworthy that a great re- 

 duction in the number of stomach worms present occurred in all of 

 the lots after the first of November, as a rule only a comparatively 

 few individual worms being found instead of the usual thousands 

 found in the lambs or ewes examined earlier. There were no im- 

 portant differences between Lot A (continuously on one pasture) and 

 Lot B (two weeks alternately in each of two pastures) with reference 

 to hookworms, nodular worms, lungworms, and tapeworms. The 

 lambs of Lot C (grazed separately from their mothers and moved 

 every week to fresh ground or ground not recently grazed) showed 

 hookworms in only one case and then only two specimens; they had 

 few or in some cases no nodular worms or worm nodules, no tape- 

 worms, and no lungworms. The lambs of Lot D (grazed with their 

 mothers on fresh pasture every week) also had comparatively few 

 hookworms, nodular worms, and worm nodules (but more than in 

 Lot C). Only one had lungworms and none tapeworms. 



These experiments apparently indicate that the plans followed as 

 to change of pastures can not be depended upon to control parasitic 



