6 INTRODUCTION. 



In the domain of pathology we find many observers 

 differing in their descriptions of well-known lesions. 

 What scientific man engaged in the investigation of 

 the markings of the diatomaceas agrees with others as 

 to their true interpretations, at the present day Ag- 

 nosticism is the only name expressing the condition of 

 men's minds on some of these subjects. Thousands of 

 questions hitherto unsettled on account of errors of 

 description, or want of agreement between observers, 

 are sure to find an easy solution if the practice of 

 photography becomes more universal among natural- 

 ists and our professional brethren. 



I do not wish to lead others to infer from this, 

 that the photographic image may not be false if 

 improperly obtained, but it can neither add anything 

 to, nor take anything from, the structure, and may be 

 relied on to shew what was actually seen by the 

 observer. 



In teaching Histology, Pathology, or any subject 

 in which the microscope plays an important part, a 

 photograph of the object may be thrown on the 

 screen in the usual manner, and the lecture proceed 

 uninterrupted by the use of separate apparatus, or 

 the time taken up by those manipulations which 

 must be made for every different observer. 



It is unnecessary to dwell on the fascination of the 

 pursuit, or the recreation afforded to those who after 

 the arduous duties of the day, relieve the strain by 

 the study of microscopy, for from what has been 

 said the advantages of photography to the Histolo- 

 gist, Pathologist, and student of Natural History, 



