Occurrence. 661 



An embryo in the central nervous system reaches the size of a pea 

 in about 24 days, and scolices are first found about the 38th day. About 

 three months are required for the full development of the cyst. 



Views are somewhat divergeut regarding the migrations of tlie embryos. One 

 view is that the embryos provided with booklets migrate into the connective tissue, 

 probably around the blood vessels and enter the cranium by the foramen lacerum. 

 This view is supported by the fact that after experimental infection minute tracks 

 are found in the loose tissues of the thoracic and abdominal organs (Baillet) and 

 also the fact that the first symptoms make their appearance after a week. As an 

 explanation as to why the cysts principally develop on the upper surface of the 

 hemispheres one must suppose that the emljryos are able to develop more easily 

 there because the furrows between the convolutions are deeper and the pressure is 

 less. According to the other view, which is especially upheld by Moller, the escape 

 of the embryos is by way of the blood stream. The occurrence of cerebral em- 

 bolism due to worms, the' absence of perforations or inflammatory changes at the 

 base of the brain or in the dura mater support this view. The latter view is prob- 

 ably correct since there are other examples of the escape of worms from the intes- 

 tine by way of the blood. . 



The power of resistance of the eggs of the tapeworm is apparently gi'eat, 

 since eggs remain alive after the disintegration of the proglottides provided that 

 the superficial layers of the ground or the grass are sufficiently moist. Gurlt saw 

 a case of severe infestation after three weeks. The eggs do not resist desiccation 

 for long and according to Roll desiccation for two weeks in the open air kills 

 them Experience shows that infestation is rare in animals that are stall ted, 

 because there is little opportunity for the contamination of food or drinking water 

 with the feces of dogs under these circumstances. The resistance of the cysts is 

 still less. According to Perroneito they are killed by raising the temperature to 

 38° to 41° C. and then cooling. 



Natural infection is due to the ing-estion of grass or water 

 contaminated either with the proglottides passed out with the 

 feces of a dog or with eggs of the Taenia coenurus after the dis- 

 integration of the proglottides. The disease attacks sheep and 

 other herhivora. The' shell of the egg is dissolved by the gas- 

 tric juice, and the liberated embryo commences its migration to- 

 wards the central nervous system. The tapeworm develops 

 principally in the intestine of sheep dogs, owing to the culpable 

 habit of shepherds of giving the brains of diseased sheepto 

 the dogs, and the carcasses of sheep that have not been buried 

 properly are also dug up by the dogs. 



The occurrence of the disease is naturally bound up with 

 the number of dogs, but the state of the weather, especially m 

 rainy springs and autumns, is also an important factor, because 

 the dampness favors the vitality of the embryos. Infection 

 through contaminated water may take place throughout the 

 year (Moussu). According to Diem, experience shows that the 

 disease occurs more frequently among the animals of farmers 

 whose meadows are close to the road where dogs can deposit 

 their feces. 



Susceptibilitv. The sheep is the most susceptil^le of all, 

 cattle and other' ruminants being more rarely affected. The 

 horse and many wild herbivora are only slightly susceptible. The 

 disease generally occurs in young animals, the sheep being at- 

 fected up to one vear old and cattle up to two years. Even 

 experimental infection fails in older animals save in exception- 

 al cases. The ox is an exception in that infection is not abso- 



