98 THE MICROSCOPE. 



coins ; by gently moving the glass together you will 

 cause them to separate and to roll over. The blood- 

 discs of mammals are entirely destitute of the granular 

 nucleus spoken of above. The discs of the blood- 

 corpuscles of the mammalia are double-concave in 

 form, and the dark spot in the centre is merely an 

 effect of refraction, for by adding a little water to 

 them, they gradually become flat and then double- 

 convex, the dark spot disappearing. They can be 

 made to assume the concave form again by treating 

 them with fluids of greater density than their own 

 contents. 



The white corpuscles are much fewer in number 

 than the red, usually not more than as i to 350 ; they 

 are for the most part globular in form, though subject 

 to much variation. 



In a medico-legal point of view, it is obvious that a 

 knowledge of the shape and relative sizes of the red 

 corpuscles might be of great use. Suppose, for instance, 

 that a man was brought before the magistrates on a 

 charge of murder ; certain marks of blood are found 

 upon his clothes. He insists, it may be, that they are 

 blood-stains of some bird, say a pheasant. The 

 microscope shows the form of the corpuscles to be 

 circular ; clearly, then, the stains in question are not 

 those of any bird, which has oval corpuscles. Intimate 

 acquaintance with the forms of the blood-discs of 

 many animals would decide the animal from which 

 they came. 



The microscope has been much used in the exami- 

 nation of articles of food and medicine, and has re- 

 vealed the existence of a great deal ot fraudulent 

 practices on the part of unscrupulous tradesmen, who 

 are in the habit of adulterating different productions. 

 " The happy application of the microscope," says Dr. 

 Hassall (" Adulterations Detected in Food and Medi- 



