11 



host (sheep in this case), and the parasite be found in it subsequently, 

 at a stage of growth correspondiug to the time which has elapsed dur- 

 ing the experiment. The conditions necessary for raising embryos, for 

 procuring uninfected sheep and for keeping them from outside sources 

 of infection, are many and difficult to fulfill. Up to the present time, 

 with few exceptions, infection has been secured in the experiments only 

 by excluding or regulating certain of the conditions surrouuding sheep. 

 These conditions are such that, although the problems in each case 

 have not been absolutely proven, there is much probability that the life- 

 history of most species is well determined. In describing the injury 

 wrought by the parasite and the resulting disease, technical descrip- 

 tion has been avoided as much as possible, in order that the work may 

 be rendered more valuable for farmers and ranchmen, who have but a 

 limited knowledge of the terms used in medical literature. These de- 

 scriptions are, on this account, necessarily imperfect from a scientific 

 point of view, but it is hoped none the less efficient for the purpose* 

 A careful study of the various diseases will show that the irritations 

 set up and the lesions resulting therefrom are mainly due to mechan- 

 ical causes, whatever be the organ attacked. Certain of the dis- 

 eases, however, seem to be aggravated by nervous or reflex irritation 

 induced by the parasite, while others are hastened by a loss of blood or 

 nutritive material abstracted from the host by the parasites. 



The diagnosis ofpayasitic diseases is always determined by finding the 

 parasite or its eggs. The quickest and surest determination for inter- 

 nal parasites is made at a post-mortem examination. For intestinal 

 parasites many authors recommend the examination of the dung. This 

 method has not been verified by experience, but appears to be tedious 

 and difficult, and a method better adapted to experts than layman. 



There are certain symptoms from which one may infer that sheep are 

 infected with parasites. A large part or all of the flock is affected and 

 the symptoms shown by the different individuals are similar. The ap- 

 petite is generally good, but individual members present a poor, stunted, 

 hidebound, bloodless, big-headed, pot-bellied appearance. Other local 

 symptoms, depending on the organs affected, are present. The most 

 positive characteristic is to find that a number of sheep raised together 

 are affected in the same way. From these general symptoms those de- 

 pending on climatic changes, and irregularity or insufficiency of food 

 and water, mustof course be excluded. The sheep owner who discovers 

 weakness among his lambs should not wait until one of them dies before 

 he endeavors to make a diagnosis, but should undertake to diagnose the 

 disease in the earlier stages by sacrificing one or more of the worst 

 affected, and thus gain time in treating and preventing the extension of 

 the disease. ByVaiting for the disease to develop he allows the lambs 

 to grow poorer and weaker, and when action is finally undertaken it is 

 upon patients which are, in many cases, already too weak to stand 

 vigorous treatment, and which can in no way profit by preventive 



