1/4 1I() \V TO WORK 



that bacteria were but the modified particles of certain tissues, 

 although the evidence really points the other way. Perfect looking 

 bacteria may be produced readily enough by gently warming over a 

 spirit-lamp a little blood placed on a glass slide and covered with 

 thin glass. From the red blood cor-puscles under these circumstances 

 numerous very narrow-jointed filamentous processes are seen to 

 project, and from their constant vibration and molecular movements 

 these might be easily mistaken for living bodies, pi. XLI, figs. 

 260, 262. Sometimes they become detached and move about in a 

 manner much resembling certain forms of bacteria. At the same 

 time any one familiar with investigations of this kind would be 

 deceived neither by the general appearance nor by the movements of 

 these bodies. Living bacteria, like other living things, come from 

 germs formed by pre-existing living things like themselves. 



The student will learn many most important facts by watching 

 the germination of the common mildew, and studying the different 

 appearances of the plant when developed under different circum- 

 stances, pi. XLI. It is exceedingly instructive to watch the growth 

 of the spongioles of a young plant (mustard seed, wheat, mignonette, 

 or better, any much smaller .->eed), as they grow under the thin 

 glass. Fluid may be constantly supplied according to the plan 

 described in page 6,7. 



By dint of a little really careful observation the stude-nt will soon 

 learn to distinguish purely vital phenomena from mere physical and 

 chemical changes, and will be able to answer the arbitrary dicta of 

 those who persist in looking upon phenomena which have nothing 

 whatever in common, as of the same nature and due to the same cause. 

 Would not any other conclusion have afforded support to the views 

 they have adopted concerning what has been termed unity ? 



OF THE EXAMINATION OF ROCKS, CRYSTALS, AND FOSSILS.* 



265. Of the Anatomy of Crystals. In the first place it is most 

 important that an observer should make himself acquainted with 

 what may be called the anatomy of crystals. Much might be said on 

 this subject, and much remains to be learned. A crystal in its most 

 perfect state is bounded by definite and perfect planes, and has an 

 uniform and simple structure throughout, as shown by its cleavage 

 or by its optical characters ; but, though the external form may be 

 very simple and perfect, its internal structure may be far from 



* For the observations upon the examination of rocks and crystals, including 

 265, 266, 267, 268, and 269, I am indebted to the kindness of my friend 

 Mr. H. C. Sorby, F.R.S. 



