BACTERIOLOGICAL EXAMINATION 293 



a septic disease or a tuberculosis, etc., to be present, and malaria has not been 

 recognized as the true cause of the morbid phenomena. [In this country the 

 opposite mistake is more common. Many cases of tuberculosis are miscalled 

 malaria because they have chills, and no proper examination of the chest or 

 of the blood is made. — Ed.] 



Among all the methods of blood examination used in the last decade un- 

 questionably the most far-reaching results have been attained by the investi- 

 gation of the NORMAL AND PATHOLOGICAL HISTOLOGY of the blood ; this was 

 particularly fostered by the technic of tlae dried preparation and the differ- 

 ential stains introduced by Ehrlich. 



If a drop of fresh blood is placed under the microscope, enlarged about 

 500 times and examined with an oil immersion a number of important points 

 may be observed. There will first be noted, provided the layer of blood is 

 thin enough, the shape of the red blood-corpuscles, their depression, their 

 hemoglobin staining; by this method also the rouleaux formation of the blood 

 discs becomes plain. The structure of the white corpuscles may be recognized 

 by this simple process, and various forms may be differentiated from one 

 another. 



Thus the lymphocytes are perceived as cells about the size of a normal 

 red blood-corpuscle, though some attain double or even three times this size; 

 their nucleus is circular, takes up the greater part of the cell, and is sharply 

 demarcated from the narrow protoplasmic border surrounding it. 



The majority of the leukocytes are conspicuous by their dense, decidedly 

 refractive, fine granulations; one, two, or three faint nuclei deposited in them 

 may be recognized. These cells are twice or three times as large as the 

 erythrocytes. In a few of the leukocytes present (eosinophiles) the granula- 

 tions are much more decidedly refractive, and the individual granules are 

 much coarser. These two last named forms are alike in size, as well as in the 

 conditions and the number and shape of their nuclei. 



The hlood'plaqiies are most easily recognized by their agglutination in 

 clumps and slight refractive power. 



Studies of the more minute structure of the leukocytes can only be made 

 with difficulty by this simple method, as the forms not yet described are 

 usually only present in very small numbers. Moreover, in a prolonged exam- 

 ination, the blood soon suffers changes which produce disturbance. In con- 

 sequence of this the investigation of the fresh blood is of very little service, 

 and we are usually compelled to preserve the blood by a proper method and 

 to stain it. For these purposes there is no better process than the dried 

 STAINING PROCESS after Ehrlich [except the methylic alcohol fixation described 

 below.— Ed.], and this is as simple in its operation as it is serviceable. It 

 has the practical advantage that it allows the investigator to work quite inde- 

 pendently of the presence of the patient, to choose the time and place of 

 examination, and permits at any time a repetition of the investigation and 

 a demonstration of the result obtained. 



The specimen is made as follows: Cover-glasses of about 18 mm., having 

 a quadrangular shape and of special thinness (0.1 to 0.08 mm.) are used; 



