OF THE BLOOD. 213 



This subject becomes the more interesting, so much reasoning 

 in the theory of medicine being built on the properties of 

 those particles. 



It is by the microscope alone that we can discover these 

 particles ; and as some dexterity and practice are required in the 

 use of that instrument, there have not been wanting men of 

 character and ingenuity, who, having been unsuccessful in their 

 own experiments, have questioned the validity of those made 

 more fortunately by others. Some have gone so far as to as- 

 sert that no credit can be given to microscopes; that they 

 deceive us, by representing objects different from what the} 

 really are (xcn). 



These assertions, though not entirely without foundation, 

 when we speak of one sort of microscopes, are very unjustly 

 applied to them all. In compound microscopes, when the 

 object is viewed through two or more glasses, if these glasses 

 be not well adapted to the focus of each other, the figure of 

 the object may be distorted ; but no such circumstance takes 

 place when we view an object through a single lens. All who 

 use spectacles agree, that the figures of objects appear the same 

 through them, as they do to the naked eye. And as the single 

 microscope has, like the spectacles, but one lens between the 



(xcn.) The differences in the results obtained by the use of the 

 microscope have often been cited, especially by Dr. Bostock, to 

 prove the inutility of this instrument in anatomical and physiological 

 inquiries. But, on the same principle, the use of the naked eye 

 might be objected to ; for there are observations made by it nearly or 

 quite as discordant as those which have resulted from the use of the 

 microscope. Let any one, for example, attend to the descriptions given 

 by various eminent men, who have used the naked eye only, of the inti- 

 mate structure of the bones, or of the filamentous and adipose tissues. 

 Yet these very subjects have been made so clear by the aid of the 

 microscope, that no anatomist is now likely to fall into the old error of 

 confounding these two last-named tissues, or, in distinguishing them, 

 to find it necessary to have recourse to the evidence of remote physio- 

 logical and pathological phenomena. "With the microscope, too, Harvey 

 could have shown a direct proof of his great discovery of the circula- 

 tion of the blood, which took so much time to establish by inference 

 from observations with the naked eye. A curious collection might be 

 formed of the errors of anatomical observations made by the naked eye 

 compared with the errors which have arisen from the use of the micro- 

 scope. 



