326 PRINCIPLES OF VETERINARY SCIENCE 



The "bare-lot" method of prevention in which the lambs and 

 ewes are kept separated in adjoining pastures, with a bare earth 

 lot between into which the lambs until weaned are frequently 

 turned with the ewes for sucking, has given good results. The 

 ewes and lambs are returned to their proper pastures after each 

 sucking period. Lambs so raised at the Bureau of Animal Indus- 

 try experiment station at twelve months weighed on the average 

 82 pounds, while lambs pastured with the ewes at thirteen months 

 weighed on the average only 70 pounds. On postmortem exami- 

 nation no nodular infection was found in lambs managed as 

 above, while the others were all infested. 



Trichinae are small, slender worms scarcely visible to the naked 

 eye. They live in the intestine of man and other animals. Man 

 acquires the parasite through eating fresh pork containing the 

 living larvae of the parasites. Hogs become infected through eat- 

 ing the flesh of other hogs or rats. The disease produced is 

 commonly known as trichinosis. The adult worms develop from 

 the larvae and produce embryos which penetrate the intestinal 

 wall and lodge in the muscles. Here the embryos coil up, 

 ■become encysted, and may be seen with the aid of a microscope. 



From two days to two weeks after infestation, the following 

 symptoms are exhibited by man: loss of appetite, nausea, ab- 

 dominal pain, diarrhea, and fever. After the parasites reach the 

 muscles the latter become tense, swollen, and painful. In 

 light cases recovery occurs in about two weeks; in severe cases 

 not until several months. In fatal cases death does not occur 

 until several weeks after the patient ate the infested pork. 



The symptoms of trichinosis in hogs are slight and usually 

 pass unnotrced, for hogs do not die of the disease. 



Since nearly 2 per cent, of all hogs in this country are affected 

 with trichinosis, it is apparent that persons should take precau- 

 tions to prevent infection. The danger may be entirely avoided 

 if pork is thoroughly cooked. By refraining from eating pork in 

 the raw state, including dried or smoked pork products, man need 

 have no fear of contracting trichinosis. 



INSECTS 



Lice are small, wingless insects. The females lay oval eggs, 

 called "nits," and secrete a glue-like substance that attaches the 



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