PART II. 

 STUDY OF THE BLOOD. 



CHAPTER XIII. 

 MICROMETRY AND BLOOD PREPARATIONS. 



MlCROMETRY. 



IN the examination of blood and faeces preparations, especially 

 when the identification of animal parasites is in question, there is 

 nothing that assists more than a knowledge of the measurements of 

 the object studied. The making of such measurements microscopic- 

 ally is termed micrometry. 



Micrometry is also indispensable in bacteriology and cytodiagnosis 

 as well as in animal parasitology. 



The most practical way of making these measurements is with an 

 ocular micrometer. These can be bought separately, or a glass disk 

 (disk micrometer) with lines ruled on it can be dropped into the ocular 

 to rest on the diaphragm inside the ocular. The ruled surface of this 

 glass diaphragm should be placed downward. As was stated in con- 

 nection with the microscope, the image of the object is formed at the 

 level of the diaphragm rim inside the ocular, consequently the lines 

 of the image cut those of the lines ruled on the glass in the ocular. 

 Once having standardized the value of the spaces of the ocular microm- 

 eter for each different objective, all that is necessary subsequently in 

 measuring is to count the number of lines or spaces which the image 

 of the object fills and then, knowing the value of each space for that 

 objective, to multiply the number of spaces by the value of a single 

 space. 



The unit in micrometry is the mikron. This is usually written /* 



