TRICHOSTRONGYLIN^ 277 



fectecl and noninfected animals together in clean fields from the first 

 of November until March. 



During the warmer months the best means of controlling the parasite 

 seems to be by the rotation of pastures, keeping each pasture free from 

 sheep and cattle for at least a 3'ear, by which tmie the larvffi will be dead. 

 As to this method Ransom (U. S. B. A. I., Cir. No. 102) suggests the 

 following: "Infested and nonmfested sheep which have been kept to- 

 gether in clean fields from November to March or later, according to 

 weather, if moved then to another clean field may remain there nearly 

 the entire month of April before there is danger of infection. From the 

 first of Ma}' on through the summer the pastures become infectious much 

 more quickly after infested sheep are placed upon them, and during 

 May it would be necessary to move the sheep at the end of every two 

 weeks, in June at the end of everj^ ten days, and in July and August at 

 the end of each week, in order to prevent the noninfected sheep from 

 becoming infected from the worms present in the rest of the flock. 

 After the first of September the period maj^ again be lengthened." 



The difficulties and inconveniences of this method consist in the num- 

 ber of small pastures and subdivisions of pastures which it requires; 

 furthermore, it imposes limitations upon the size of the flock. It is, 

 however, probably the most effective system thus far devised for the 

 eradication of this parasite. 



Where it can be convenientl.y practiced, it is a good precautionarj^ 

 measure to burn over the pastures in the early spring or fall. This will 

 destroy most of the eggs and larvae which are lodged upon the grass or 

 upon the ground. 



Treatment. — Experiences recorded with the use of drugs for the 

 expulsion of stomach worms are somewhat varied. The success attained 

 by such treatment has not equaled expectations based upon experiments 

 made with the agents upon worms outside of the bod}'- of a host. It is 

 probable that this is mainly due to the fact that drugs administered to 

 ruminants by the mouth do not pass directly to the abomasum, but must 

 first mix with the ingesta of the rumen and reticulum, passing from the 

 latter by way of the omasum to the abomasum and intestine. Hence, 

 before reaching the worms the drug become sufficiently diluted or mixed 

 with the bulky ingesta to greatly reduce its effectiveness. Treatment 

 for the expulsion of Hcemonchus contortus gives better promise for success 

 than that for the smaller stomach strongjdes, as Ostertagia ostertagi, 

 owing to the protected position of the latter within the nmcosa. 



Animals which are to be treated should be taken up in the afternoon 

 of the day previous to treatment and all food withheld from them for 

 eighteen to twenty-two hours. The remedy should be given the following 

 morning either with a long-necked bottle or, better,, with a drenching 

 tube consisting of about three feet of one-half inch rubber tubing with 



