HOW COCCIDIOSIS IS SPREAD 133 



the immediate contamination of the soil that has 

 to be feared. Worms of all varieties constantly 

 remove soil from place to place ; moles and ants 

 aid in renewing the surface and in transportation; 

 rabbits scattering through heather or other vegeta- 

 tion raise a dust-mist around themselves ; and by 

 many other animals, soil or faeces rich in coccidian 

 cysts are scattered over the face of the country. 



The wind carries the dust hither and thither, and 

 when it falls, the cysts are deposited on growing 

 heather and in tarns and streams indiscriminately. A 

 rainstorm aids in the process, and deadly faecal matter 

 is washed into the water-supply so necessary for the 

 vigorous growth of the young animals. Feeding on 

 the juicier young heather-shoots or drinking at their 

 favourite shallow pools, the chicks swallow the 

 spores, and if these are present in any numbers, in 

 about eight to ten days' time the young covey will 

 have disappeared, slain by the unsuspected enemies 

 absorbed with their food. 



Wind, food, and water are not the only means 

 of spread of disease. Occasionally veritable flying 

 parasite carriers are encountered in the form of 

 birds which have been infected, but have by some 

 means adapted themselves to the presence of the 

 parasites, and are, to all intents and purposes, not 

 inconvenienced by them. Such birds may be termed 

 " chronics." They are always infected themselves, 

 and periodically void faeces heavily charged with 

 cysts, yet externally they appear healthy. Rarely 

 are symptoms such as thinness, anaemia, or poor 

 feathering marked. But such birds are a very real 



