264 THE GROUSE IN HEALTH AND IN DISEASE 



retained the power of infecting birds, as I have been able to show experimentally. 

 Such material contains undifferentiated oocysts still, while its outer layers mainly 

 contain oocysts with four sporocysts within them. 



(y) Development under Different Conditions of Temperature. 



For experimental purposes, it was sometimes necessary to delay the development 

 of sporocysts. This was easily done. The oocysts in faeces were transferred to a 

 chamber kept at 10 degrees C., having been previously kept at 15 degrees C. This 

 change was sufficient 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 occur- 

 rence of occasional outbreaks of disease after the first attack had passed off. 

 Moisture and coolness retard the development of certain oocysts for a considerable 

 time, during which period the disease disappears. A return of conditions favour- 

 able to the Coccidium then ensues, rapid development of sporocysts occurs, and 

 a fresh outbreak of disease is initiated. 1 



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 August that it 

 is discovered that there is a scarcity of young birds, and various hypotheses are put 

 forward to account for their mysterious disappearance (vide chapter ii. pp. 14-16). 

 It is significant 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 caused the bird to die from 

 want of water. We now know that young Grouse chicks seldom, if ever, die of 

 thirst, 2 whereas we also know that dry heat is not unfavourable to the develop- 

 ment of the oocysts. 



VIII. EFFECTS OF CERTAIN REAGENTS ON COCCIDIAN OOCYSTS. 



Certain experiments were made with a view to finding a means of destroying 

 oocysts without killing all other forms of life. 



This is not an easy matter. While such strong reagents as caustic potash will 

 slowly dissolve the oocysts, their application is not practicable on Grouse moors. 



1 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. 



2 Vide chap. iv. pp. 93-94. 



