OBSERVATIONS ON THE BLOOD OF GROUSE 309 



even when the factors noted in the preceding paragraph have been considered. 

 Nevertheless, the correlation of the numbers and condition of the blood-elements, 

 particularly of the leucocytes, with the occurrence of specific protozoal and 

 helminthic parasites, renders an examination of the blood a most useful adjunct 

 in investigating somewhat obscure diseases. Several protozoal parasites (vide 

 chapter xiv. p. 318), are present in Grouse, both in the blood and in the gut, and 

 the condition of the bird's blood can be correlated with the presence of some of the 

 individual parasites. 



Blood taken from a winw vein was used in the case of livino- birds, of which 

 twelve were thus examined. In the case of freshly killed Grouse, blood 



•^ Methods. 



taken directly from the heart was employed. The usual methods and 

 precautions were followed in securing suitable drops of blood for examination. 



Hayem's fluid was used as a diluent for counting the red cells of the blood, 

 while Toison's fluid was used in the case of the leucocytes. 



The Thoma-Zeiss hjemocytometer was employed. The disc of the counting 

 chamber was ruled according to Zappert. 



A dilution of at least 200 or 250 was found to be necessary for counting the 

 red cells, and a dilution of 20 to 25 was absolutely necessary in counting the 

 leucocytes. Sometimes a dilution of 100 was taken in counting the leucocytes, 

 and this greater dilution was often preferable. 



For differential leucocyte-counts blood-smears were made on both cover-slips 

 and slides, especially the former. 



The stain generally used in making preparations for differential counting was- 

 that of Jenner. Occasionally Giemsa's stain was employed. 



The elements present in the blood of normal Grouse may be grouped as : 



(a) Erythrocytes. Cells in 



n \ r normal 



(o) Leucocytes. blood. 



(c) Thrombocytes. 



The leucocytes are further subdivided, and may be grouped as mononuclear, 



polymorphonuclear, and eosinophile leucocytes, and lymphocytes. Mast cells, 



which are markedly basophile, are also present. Erythroblasts also may be 

 encountered. These forms may now be considered separately. 



(a) Erythrocytes. — These are the most abundant elements in the blood. The 

 erythrocytes or red blood corpuscles are oval in contour (PI. XLV., Fig. 1). They 



