560 DISEASES OF CATTLE, SHEEP, GOATS, ETC. 



with the feces. Under favorable conditions these eggs are washed 

 onto the grass or into standing or running water, and sheep eating 

 grass or drinking water so infected thereby take the eggs into the 

 stomach. Here the shell digests off and a very small embryo, armed 

 with six hooks, bores its way through the walls of the digestive tract 

 by means of these hooks, gets into the blood vessels, and is swept 

 around till it lodges. In any location except the brain or spinal cord 

 the parasite may grow to the size of a pea, but at that point or sooner 

 it degenerates and dies. Those that get to the brain or spinal cord 

 develop into the bladderworm described above. 



At the time when the embryos get to the brain and begin to 

 travel on its surface or through its substance there are usually slight 

 symptoms of fever and restlessness, which are easily overlooked. 

 Should the infection be severe enough to kill the sheep at this stage, 

 an examination of the brain will disclose a number of curving chan- 

 nels on its surface. But as a rule these symptoms abate and there is 

 no further indication of the presence of the parasite until it has 

 grown to the point where the heads form on the bladder and set up 

 the symptoms characteristic of the last stages of gid by projecting out 

 of the bladder and into the brain. This is accomplished by virtue of 

 the fact that the head is seated at the bottom of a little tubular neck 

 with an opening to the exterior. Ordinarily this neck projects into 

 the bladder fluid; but the head and neck can be projected through 

 the opening mentioned, the neck turning inside out, just as a glove 

 finger might be turned inside out. When the head is pushed out it 

 brings the crown of hooks with which it is armed into contact with 

 the brain, and it is to the irritating action of these hooks on the brain 

 that such symptoms as walking in a circle are ascribed. It seems 

 probable that only such symptoms as circling or running or jumping 

 without apparent cause, which are of an intermittent and occasional 

 sort, should be referred to the action of the tapeworm heads. Such 

 symptoms as are constant in the last stages of the disease, including 

 blindness, constant carriage of the head to one side, loss of appetite, 

 and the like, should probably be referred to atrophy of the brain due 

 to the pressure of the parasite, and to other nervous disturbances re- 

 sulting from this pressure. 



The final symptoms of gid do not show until seven or eight 

 months after the sheep has become infected, the sheep usually dying 

 about nine months aftej the time of infection. This point is im- 

 portant, because the Montana sheepmen, being unacquainted with 

 the true nature of the disease, have been inclined to attribute gid to 

 the nature of the country in which the sheep were feeding at the 

 time of the outbreak, and it is difficult to convince them that the in- 

 fection was more or less remote from the range where the outbreak 

 occurs. 



LIFE HISTORY IN RELATION TO MONTANA CONDITIONS. 



The actual history of the disease in most cases in Montana seems 

 to be about as follows : The developed larval parasite, capable of in- 

 fecting the dog, is found in sheep mostly while on the winter range 

 from December to the end of March, exceptional cases occurring out- 



