BACTERIOLOGICAL EXAMINATION 301 



the stained dry preparation. For this purpose we use the movable quadratic 

 Ehrlich eye-piece (see Fig. 20). The principle of this diaphragm depends 

 upon its making it possible to count the red and white blood-corpuscles in 

 different large divisions of the field of view, so that, for example, the leuko- 

 cytes are counted in A field six or nine times as large as the field in which the 



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Fig. 20. — Ehklich's Eye-piece with Ikis Diaphragm. 



reds are counted. The total number determined after counting a larger series 

 of fields of the red is then directly compared with the sum of the white by 

 multiplying by six or nine. A prerequisite for a correct result by this method 

 of estimation is an absolutely uniform layer of blood upon the cover-glass. 



The proportional relation of the individual varieties of blood-corpuscles 

 to one another may be determined by a simple calculation of the cells when 

 examining a dry preparation. 



We have described the fundamental characteristics of the blood cells in 

 their normal and pathological condition, omitting everything that depends 

 upon purely theoretic investigation and which has not yet been directly applied 

 to practice, as well as that which is still being debated, and concerning which 

 the views of competent observers are still at variance. How has it been possi- 

 ble to utilize this material in general and special pathology? 



In the article upon Anemia (see this volume) due stress has been laid upon 

 the pathological changes which the red blood-corpuscles undergo in the various 

 anemias, and we may now limit ourselves to a description of the changes in the 

 white blood cells in the same diseases. 



In the first place, as regards the appearance of pathological cell forms, 

 for the reasons indicated we have included only the myelocytes in our descrip- 

 tion. But the circumstances under which these are found in the circulating 

 blood agree in so many points with the circumstances under which the num- 

 ber of white blood-corpuscles increases or decreases that they require no 

 special elucidation. 



Consequently, the most important chapter in the pathology of the white 

 blood-eorpuscles is that which treats of the changes in their total number and 

 the relative proportions of the individual leukocyte forms. Since, in general, 

 we refer to the presence of leukocytes as leukocytosis, an increase of their 



