OPERATIVE SUEGERY. 301 



in other parts of the system by a process termed metastasis, 

 making such gTowths one of the most dangerous and unsatis- 

 factory conditions to deal with which affect animal life. Further 

 mention will not be made of any special class of tumor liable to 

 affect the sheep, with the exception of goitre, which will now be 

 considered. 



Goitre. Struma. 



This is an affection of the thyroid glands, in which they be- 

 come enlarged, sometimes to such an extent that the functions 

 of the trachea and oesophagus become interfered with, so as to 

 threaten the subject's existence. It may exist in any one of 

 four forms, viz: 



(1) Real Goitre, when the swelling is due to enlargement 

 of the gland follicles, the whole gland or only part of it being 

 involved. 



(2) Fibrous Goitre, where the connective tissue of the 

 gland is increased, the follicles remaining normal or nearly so, 

 portions of the gland as a rule only being affected. 



(3) Dilatation of the veins, or vai'icose goitre. 



(4) Cystic Goitre- — or bronchocele. This last form is 

 that generally found affecting sheep, lambs more especially, and 

 is supposed to be due to the presence of magnesia in the drinking- 

 water. 



Goitre is a common affection of the human family as well a? 

 animals, and up to the present time the causes do not appear to 

 be very well understood. The locality appears '"o have a predis- 

 posing effect. Williams states that animals grazing on soil rich in 

 magnesian lime are prone to this affection. As it attacks ani- 

 mals, sheep especially, lambs appear to be more subject to the 

 condition than mature sheep. Heredity appears to have a strong- 

 relation to the transmissibility of the disease, instances having 



