260 THE GROUSE IN HEALTH AND IN DISEASE 



layers rapidly develop sporocysts, the inner ones remaining 

 unaffected. 



It has been proved experimentally that soft droppings kept 

 en masse in covered dishes for as long as twelve months l have 

 retained the power of infecting birds. Such material contains 

 undeveloped oocysts within, while its outer layers mainly 

 contain oocysts with four sporocysts. 



(c) Development under Different Conditions of Temperature. 



It was found that when the coccidian cysts were transferred 

 from a chamber, kept at 15 degrees C. to a temperature of 10 

 degrees C. the effect was to delay all further development for 

 a considerable time. Smaller changes of temperature also 

 arrested the development of sporocysts, though the effect 

 naturally was not so marked. 



Changes of temperature and moisture on the moors might 

 result in the occurrence of occasional outbreaks of disease 

 after the first attack had passed off. Moisture and coolness 

 would retard the development of certain oocysts for a consider- 

 able time, during which period the disease would disappear. 

 A return of conditions favourable to the Coccidium then ensues, 

 rapid development of sporocysts occurs, and a fresh outbreak 

 of disease is initiated. 2 



Unfortunately, it is difficult to follow the course of the 

 disease under natural conditions on the moors ; the greatest 

 mortality occurs among very small chicks, and the dead bodies 

 are rarely found. It might be possible for nearly every Grouse 

 chick on a moor to die without the owner or his gamekeepers 

 being aware of the fact. In such cases it is only when the 

 stock is inspected in July and early in August that it is 

 discovered that there is a scarcity of young birds. It is signifi- 

 cant that one of the causes most commonly given is drought, 

 i.e., that a long period of hot, dry weather in May and June has 



1 Further experiments have shown that some coccidian oocysts can retain their 

 vitality for two years. 



2 It is possible that the second outbreak of the disease will not be so fatal as the 

 earlier one, owing to the increased age of the birds. 



