STOMACH WORMS IN LAMBS AND THEIR CONTROL         273

                                                    TABLE IV.

Showing the total numbers of worms recovered from the abomasums of the progressional
                                    and non-progressional groups. 

                                 DISCUSSION OF RESULTS.

In the case of H. contortus the total number of worms recovered from the six
lambs of the non-progressional group was 1,550, or an average of 258 per lamb.
From the progressional group only 12 worms were recovered, giving an average of
2 per lamb. These results show that progressional grazing was efficient to the
extent of reducing H. contortus infestation 99.2 per cent. compared with the non-
progressional group. In other words H. contortus can be completely controlled by
this system.

The average number of O. circumcincta recovered from the non-progressional
and progressional groups was 865 and 166 respectively, giving an efficiency of 80.8
per cent. The lower percentage of reduction in the case of 0. circumcincta would
point to the fact that some larvæ were able to reach the infective stage in less than
10 days. For all practical purposes, however, 10 days may be considered a safe
period for this species, as the few larvæ that may develop to the infective stage
within that time are not likely to cause much harm.

Statistical analysis of these results kindly undertaken by Dr. Tocher, Aberdeen,
indicate that the odds against the results being fortuitous are 700 to 1, and 1,000 to
1 for H. contortus and O. circumcincta respectively.

The number of worms recovered from the non-progressional group indicate the
degree to which lambs may become infested when put to graze on worm-free

                                                                                                        G 2