CHAPTER V. 



NORMAL H^MATOLOGY. 



INTRODUCTION. 



THE examination of the blood, like that of the urine, gives a posi- 

 tive diagnosis in a number of diseases. It assists the diagnosis in 

 many diseases and is often of much value negatively. It is important, 

 then, to be familiar with the characteristics of normal blood. The 

 examination of the normal blood consists of an actual study of the 

 blood by use of the microscope and the determination of many of 

 its properties by the use of various instruments, which will be 

 described in the text. The accurate use of the instruments can be 

 learned only by experience. While the instruments are delicate and 

 easily broken, yet the technique of their use is easily mastered by 

 the student if he is careful, accurate, and persevering. The technique 

 once acquired can be quickly regained in later years, although it 

 may apparently be forgotten for the time being. Speed in the tests 

 can be obtained only by continuous practice. Theoretically all these 

 instruments are accurate, but because of the minute quantity of 

 blood used, slight inaccuracies will be multiplied in the final results 

 and may be large or small according to the experience and careful- 

 ness of the observer. By knowing where these errors are possible 

 and avoiding them by the best-known methods, and by adopting a 

 definite method of use of each instrument, these inaccuracies can 

 be largely eliminated and good comparative results obtained. In 

 the use of blood instruments the observer must constantly avoid 

 manufacturing results. There is always the tendency to read into 

 the test a preconceived result. This is best governed by control 

 tests and by repeated tests. When one can repeat a test three or 

 four times with the same individual's blood and obtain approximately 

 the same results he is quite proficient. 



REFERENCE BOOKS. Clinical Examination of the Blood, by Cabot. Clinical Pathology of 

 the Blood, by Ewing. Clinical Haematology, by Da Costa. Histology of the Blood, by Ehrlich 

 and Lazarus. Text-book on Physiology, by Hall. Works on Histology and Physiology. 



GENERAL DIRECTIONS. 



All blood instruments must be perfectly clean and dry if the best 

 results are to be obtained. The various pipettes are cleaned by the 

 use of hydrogen peroxide and distilled water; they are then dried 



