PREVENTIVE MEDICINE 343 



eggs mature, and this explains the heavy infestation of flocks after 

 wet seasons. Mature larvae stored on the ground are able to pass 

 the winter without heavy mortality. 



PREVENTIVE MEASURES consist of efficient anthelmintic treat- 

 ment, good feeding, with an addition of salt to the ration, an 

 abundant supply of pure water and avoidance of stagnant pools. 

 It is advisable that the animals should be housed with the object 

 of restricting pasture contamination. All litter should be burnt. 

 The pastures should be sprinkled with lime or salt, or be ploughed 

 up. Hay from such pastures should be fed to animals which are 

 not susceptible, e.g., horses. 



FLIES. 



Limitation of space does not permit of a detailed account of 

 the numerous flies that are of importance to the veterinary hygienist 

 in the British Isles. The reader is referred to the article by Noel 

 Fillers in W. Hoare's System of Veterinary Medicine. 



Biting and sucking flies worry all animals, horses and cattle 

 especially, not only by their actual contact, but by their mere 

 presence. The stable fly, Stomoxys calcitrant, which is a blood- 

 sucking fly, is common in stables and byres from the spring until 

 the autumn. It is very annoying to all stabled animals, and 

 especially to the sick. 



It has been shown that the presence of a number of flies in a 

 cow byre reduces the milk yield of the cows. The common house 

 fly, Musca domestica, is beyond any doubt responsible for the 

 dissemination of disease, and every effort should be made to destroy 

 it in all stages of its existence. 



The danger of the common house fly to man and also to animals 

 is due to the fact that it is born in filth and spends its brief but 

 active life paying a constant series of calls from filth to food 

 and food to filth. As the filth may, and often does, contain patho- 

 genic bacteria, and as the fly is so constructed that when it alights 

 on filth much of the latter adheres to it, it is not difficult to realise 

 its potential danger. 



The metamorphosis of the common house fly takes from a 

 week to a fortnight, or much longer in cold weather, the stages 

 of development being, egg to larvae or maggot, maggot to pupa, 

 and pupa to adult. Warmth is necessary for the development of 

 the larva from the egg, hence fermenting material, such as manure 

 or decaying animal or vegetable matter, is always chosen by the 

 stable fly and the house fly for oviposition. 



