PREFACE. 



No apology seems to be necessary for this book. So far as 

 I know, no attempt has been made by any person apparently 

 up in the subject to give instructions for Photo-micrography, 



ERRATA. 



The titles of Plates IV. and V. have been trans- 

 posed. Thus : IV. i is Pneumococci encapsuled x 

 500 ; V. i is B. Anthracis in Blood x 750, etc. 



Plate VI. i is B. Tuberculosis by Inoculation x 

 600, while VI. 2 fe B. Tuberculosis in Lung of Horse 

 x 750. 



Page 71, line i, for "125 " read " 25." 



have written something that will materially help those who 

 study the Natural Sciences in general rather than Optical 

 Science in particular. 



I have to thank many friends for help of various kinds. 

 Mr. Edward M. Nelson, my instructor in practical microscopy, 

 has placed me under the most marked obligation, for he kindly 

 read my M.S. so far as it touched optical theories, and he 

 directed me where necessary. I owe so much generally to 



