DISEASES OF SHEEP. 93 



ermination of the disease. It is sure to ensue when the 

 nalady is in its advanced stages, but in mild cases recovery 

 ometimes takes place. Many sheep gnaw their skin and 

 -ppear somewhat lame in the croup; 'and after this has 

 asted for several weeks, without other symptoms of disease, 

 t disappears of its own accord. Such favorable cases must 

 Iways be considered as exceptions to the rule. The dura- 

 ion of the disease, from the first visible symptoms until it 

 erminates in death, is generally from two to three months. 

 Some, however, die earlier, and others, especially if they 

 ,re well-cared for, much later. On dissection I always 

 bund a little water in the cavity of the spinal canal, es- 

 )eciaily in the region of the last lumbar and first crucial 

 vertebrae. I often found the spinal marrow softer, and in 

 are cases harder, than in its normal condition, and a portion 

 if it had wasted away. A little water was also generally 

 bund in the brain, and the other parts were unchanged and 

 lealthy. Sometimes a worm-blister was found in the spinal 

 :anal, analogous to that observed in the brain in vertigo, 

 lut this must be considered as an exceptional symptom. 



The first cause of the disease is not definitely ascertained, 

 lut recent observations have shed considerable light on the 

 ubject, so that a certain result may be hoped for. It has 

 leen discovered that the gnaw disease occurs but rarely in 

 'ears when the vertigo prevails, and vice versd. This cir- 

 umstance leads to the conclusion that a certain analogy 

 btains between these diseases, both as regards their nature 

 ,nd causes. An improper method of feeding seems to have 

 tiuch to do with them, and the predisposition for the gnaw 

 lisease is undoubtedly hereditary. A cure of the disease 

 a its advanced stages is rarely ever possible, and it is 

 herefore best to turn such animals over to the butcher. 

 Jut a prevention is tolerably sure if the following rules be 

 bserved : 



