342 VETERINARY HYGIENE 



which they may graze. In many instances horse-rearing has to be 

 abandoned on farms on account of the extent to which the ground 

 is contaminated, and to the fact that the breeding stock often per- 

 sistently carry the parasites and re-infect such pastures as have been 

 rested and cleaned. " Horse-sick " ground should be grazed by 

 cattle or sheep for two or three seasons and all horses kept from it. 

 It is now known that ascaris infection can be spread through the 

 agency of rats and mice, for Stewart has shown* that the larvae of 

 A. lumbricoides and A. suilcs may be hatched out from eggs in the 

 alimentary tract of rats and mice, whence they travel to the lungs. 

 Stewart found the larvae in the trachea and bronchi and mouths 

 of these rodents on the seventh day after they were fed on the 

 mature eggs. It is therefore obvious that grain and fodder could 

 easily become infected with the larvae. In consequence the destruc- 

 tion of rats and mice is indicated. 



PARASITIC GASTRITIS. 



This is most frequently observed in calves and lambs and is of 

 greatest importance in these species, the disease often appearing as 

 an enzootic. 



Strongulus convolutus (Ostertag) is the commonest cause of 

 parasitic gastritis in cattle, though M'Fadyeanf in this country 

 encountered a much smaller worm to which he applied the name 

 Strongulus gracilis. In sheep the causal parasites are 5". contortus, 

 S. cervicornis, and others. 



The disease is especially severe in young animals, e.g., in the 

 case of cattle from 6 months to 2 years of age, the chief symptoms 

 being diarrhoea, emaciation and anaemia. In acute outbreaks the 

 mortality may be as high as 90 per cent., and the course of the 

 disease may be only a few days, but is more often 2 to 4 weeks. In 

 adult animals death may also occur, but the disease more often 

 assumes a chronic condition lasting for months or years. Cases are 

 usually seen in late autumn, winter and early spring, but may occur 

 at any time of the year, and though most frequent in wet seasons, 

 according to Penberthy, are not confined to these. 



The life history of S. contortus has been worked out recently 

 by Veglia$ in South Africa. He found the eggs and larvae to be 

 capable of considerable resistance to destructive agencies, e.g., 

 desiccation, though sunlight is the chief devitalizing factor. It 

 is only after protracted rainy weather that a large percentage of 



* Brit. Med. Journ., July, 1916, p. 5. 



f Journ. Comp. Path., Vol. IX., p. 314. 



$ Journ. Comp. Path., 1906, Vol. XXIX., p. 265, Abs. 



