248 THE GROUSE IN HEALTH AND IN DISEASE 



introduced, remain unharmed, and the cysts are merely 

 passed out of the birds in their droppings. Occasionally 

 Coccidiosis occurs as a disease in man. 



The species of Coccidium which infects Grouse is also capable 

 of infecting fowls, pigeons, turkeys, pheasants, sparrows, and 

 canaries ; indeed, it is probable that nearly all birds are liable 

 to be attacked by this parasite. Amongst poultry farmers 

 the disease is familiar under the name of " White Diarrhoea," 

 one of the symptoms being the fluid condition of the excreta 

 and the white colour given to them by the presence of millions 

 of cysts more correctly called oocysts of the Protozoon. In 

 turkeys the disease is often known as " blackhead." 



The life history of the Coccidium is extremely complicated, 

 even though, unlike some parasites, the organism completes 

 its development within one host. Its life-cycle is fully described 

 and illustrated in the first edition of the Committee's Report, 

 and it will be sufficient here to give a brief summary of the 

 changes through which the parasite passes during the period 

 when it remains within the Grouse. Reference may be made 

 to the text-figure on p. 248, which gives a diagrammatic repre- 

 sentation of these changes. 



Beginning with the oocyst, which is swallowed by the Grouse 

 with its food or water, we find that each ripe oocyst contains 

 four sporocysts (Fig. 36, S) or spores, and each sporocyst contains 

 two germs or sporozoites (Fig. 36, T). These germs are liberated 

 by the action of the digestive juices (Fig. 36, A), and rapidly 

 penetrate the delicate cells which form the lining of the gut 

 (Fig. 36, B). In these cells the sporozoite rounds up (Fig. 36, C), 

 and becomes a passive growing form or trophozoite (Fig. 36, D). 

 After a period of rapid growth, during which time the trophozoite 

 practically destroys the cell harbouring it, the parasite enters 

 upon a multiplicative phase termed schizogony. 



The parasite at this stage is known as a schizont, The 

 schizont is at first single (Fig. 36, D), but soon subdivides into 

 a number of curved daughter forms arranged within the host- 

 cell, like the segments of an orange (Fig. 36, E, F, G). These 



