2 80 HOW TO WORK 



PART V. 



OF THE HIGHEST MAGNIFYING POWERS YET MADE, AND OF THE 



BEST METHODS OF USING THEM NEW METHOD OF PREPARING 



SPECIMENS FOR EXAMINATION WITH THE HIGHEST POWERS- 

 NEW VIEWS CONCERNING THE STRUCTURE, GROWTH, AND NU- 

 TRITION OF TISSUES AND OF LIFE OF THE STRUCTURE AND 

 ACTION OF A NERVOUS APPARATUS. 



IN this the last section of my book, I propose to consider how 

 objects may be most satisfactorily examined with the aid of the 

 highest powers yet made. I shall venture to describe in detail 

 the special method which I have found it necessary to employ in my 

 recent investigations upon the minute structure of various textures 

 and the changes which take place in the course of growth. By this 

 process, sections of any tissue may be prepared thin "enough for 

 examination by powers magnifying upwards of 5,000 diameters, and 

 the vessels may be injected and afterwards displayed in the same 

 preparations. 



This part of the subject introduced for the consideration of the 

 more advanced student, should not be studied by beginners until 

 they have honestly gone through the tables at the end of the volume, 

 and have perfected themselves in the various operations there indi- 

 cated. When the elementary principles and practical details have 

 been thoroughly mastered, the observer may practice the process of 

 staining tissues, p. 107, and endeavour to make exceedingly thin 

 sections, p. 80. In this way he will be gradually led to attempt to 

 make original investigations, and, in the course of his experiments, 

 no doubt important improvements in the methods of preparation 

 now in use will occur to him. 



355. An Apology for the Use of very high Magnifying Powers. 

 Before describing the highest magnifying powers and the method of 

 using them, it is unfortunately necessary for me to allude to objec- 

 tions which have been raised to their use and endeavour to answer 

 some of them. Some persons still persist in asserting that no advan- 

 tage is to be gained from powers above 300 diameters. Now, it 

 would be impossible for me to answer all the objections that have 

 been raised to this and other methods of observation, in Germany 

 and elsewhere, and it is obvious that every observer has a perfect 



