Z INTRODUCTION. 



some favourite theory, or showing the existence of 

 some doubtful structure. 



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 diatomaceae 

 agrees with others as to their true interpretation, at 

 the present day Agnosticism is the only name 

 expressing the condition of men's minds on some of 

 these subjects. Thousands of questions hitherto un- 

 settled 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 naturalists and our profes- 

 sional brethren. 



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

 that the photographic image may not be false if im- 

 properly obtained, but it can neither add anything 

 to, nor take anything from, the structure, and rnay 

 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 



