536 DISEASES OF CATTLE. 



and attacks the red blood corpuscles. For a discussion of this para- 

 site and the disease which it produces see page 473 of this volume. 



Other parasites which live in the blood cause serious diseases known 

 as surra and nagana (p. 508) , but as yet neither of these diseases has 

 gained a foothold in the United States. 



PARASITES OF THE EYE. 



Small roundworms, one-third to four-fifths of an inch in length, 

 may occur in the ducts of the lacrimal glands. Several species all 

 belonging to the same genus {Thelazia) are known. They some- 

 times escape from their usual location and may be found on the sur- 

 face of the eyeball beneath the lids, or even in the eyeball. It has 

 been supposed by some writers that the worms seen in the interior 

 of the eyeball ("snakes in the eye") are immature stages of Setaria 

 lahiato-papillosa (see p. 534) which have gone astray from the normal 

 course of their migration, but the correctness of this supposition is 

 uncertain. 



Worms in the eyes and lacrimal ducts may cause inflammation, in 

 which case the eyes may be syringed with an antiseptic, such as a 

 weak solution of coal-tar stock dip, and iodoform ointment applied 

 if the condition is severe. 



When worms are present in the eyeball itself, their removal de- 

 pends upon surgical treatment, usually not advisable, as the worms in 

 that location either cause but little trouble or disappear withorit 

 treatment. 



