DISEASES OF. SHEEP 567 



Only the more favorable cases should be operated on. These 

 are cases where the diagnosis indicates that the parasite is situated on 

 the upper surface of the cerebrum, or large anterior part of the brain, 

 and therefore accessible from an opening in the top of the skull. It 

 is hardly possible always to locate a parasite accurately from the 

 symptoms. The abnormal movements of the sheep are believed to 

 be due to the everted tapeworm heads which irritate such parts of the 

 brain as they come in contact with and thereby set up corresponding 

 reactions. Inasmuch as a large cyst will have numerous heads capa- 

 ble of irritating the brain at relatively widely separated points, it will 

 set up correspondingly variable reactions. At the same time certain 

 symptoms will correctly indicate the location of the parasite in the 

 majority of cases. Moreover, if the parasite is located on the upper 

 surface of the brain it not uncommonly causes the formation of a 

 soft spot in the skull just over the cyst, and this can be found by 

 pressing firmly on the skull with the thumb till a place is found 

 where the skull yields a little. As a rule, when such a place is pressed 

 in the sheep will start violently. It may be that this is due to the 

 pressure on the skull being communicated by hydrostatic pressure 

 through the cyst, and thus causing the sudden simultaneous aversion 

 of all or many of the tapeworm heads. 



There are some sheep which can not be saved by operation. 

 Some of these have the parasite in an inaccessible location at the 

 base of the brain. Others have several parasites in the brain and 

 their detection and successful removal may be impossible. Still 

 others have the parasite located in the cerebellum, the small poste- 

 rior part of the brain, or in the spinal cord, and can not be success- 

 fully operated on. Finally, the operator will not always be success- 

 ful and some sheep will die of meningitis or some other complica- 

 tion. 



For the purpose of the sheepman who wishes to perform the 

 operation for gid, only those animals that circle should be operated 

 on. In a majority of these cases the parasite will be located in the 

 cerebrum near the surface and on the side toward which the sheep 

 turns. The soft spot in the skull, if present, will usually be found 

 on this side. The sheep will usually nave a peculiar stare and will 

 often run into things as if blind. 



In any operation avoid the middle line of the skull and oper- 

 ate to one side, as the main blood vessels are located in the middle 

 line. It is advisable to use a local anesthetic, such as cocain, as it 

 not only lessens the suffering of the animal, but also makes the 

 animal easier to handle and operate on as a result of the lessened 

 pain. For the purpose of injecting cocain, a hypodermic syringe, 

 with a capacity of 2 cubic centimeters, can be purchased for a 

 trifling sum. 



If a trephine outfit is used the trephine should have about a 

 five-eighths inch cut. Beside the trephine there will 'be needed a 

 knife or scalpel an ordinary pocketknife will serve, but is not so 

 easy to sterilize a pair of fine scissors with the blades bent at an 

 angle to the handle, a pair of forceps, an ordinary pair of shears, a 



