2/0 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



it is rare to find them in any considerable numbers in other 

 conditions. When you are frequently examining blood-films 

 with the same lens and eye-piece, you will soon be able to pick 

 out forms of abnormal size. When you have not had this 

 experience it is advisable to make a film of normal blood for 

 comparison, and to look first at one and then at the other. A 

 still better method (due to Shattock) is to mount the two films 

 (the normal and abnormal, both stained) face to face, and then 

 to mount the pair on a slide, and examine them with an oil- 

 immersion lens; a slight turn of the fine adjustment will 

 enable you to pass at once from the one to the other, and to 

 compare the diameters of the corpuscles with some degree of 

 accuracy. Another useful method is to employ the counting- 

 chamber of the hsemocytometer, and an idea of the diameter 

 of the reds should be gained in all cases of pernicious anaemia 

 whilst the count is being- made. The diameter of one of the 

 small squares is almost exactly six times that of a normal red 

 corpuscle. If you look at the squares with a central ruling, 

 you will be able to compare any corpuscles which may be in 

 them with the semi-diameter; the one should be one-third of 

 the other, and you may consider as a megalocyte any corpuscle 

 which is one-half or more of this semi-diameter. 



3. Poikilocytes (Plate VIII., Fig. 6) are deformed cor- 

 puscles, and are typically shaped like a pear, but may be kid- 

 ney-shaped or quite irregular. They may be about as large 

 as a normal corpuscle, or smaller, or larger, and they may 

 stain abnormally. Poikilocytes are more common in per- 

 nicious anaemia than in other diseases, but are not of much 

 diagnostic importance, since they only occur in advanced 

 stages of the disease, long after the diagnosis should have 

 been made. To recognize them, put a small drop of blood on 

 a perfectly clean slide, apply a cover-glass, and examine at 

 once; do not identify poikilocytes in dried films or in the 

 counting-chamber of the haemocytometer until you have had 

 a good deal of experience, as accidentally injured and con- 

 torted forms may occur in either. 



4. Polychromasia, or, as it was formerly called, Polychro- 

 matophil Degeneration (Plate VIII., Fig. 3). In this condi- 

 tion the corpuscle (which may be normal or abnormal in other 

 ways), instead of being strictly acidophile in its staining re- 

 actions, stains with the basic stain to a greater or less extent; 



