1884.] 



MICEOSCOPICAL JOURNAL. 



51 



Sometimes two or more rotifers were 

 seen together in the same stentor, un- 

 dergoing absorption. All movements 

 of the prey ceased when caught by 

 the Rhyopod-like extension of the 

 stentor, who did not seem at all in- 

 convenienced by the presence of his 

 neighbors within, but kept up its 

 graceful wanderings to and fro as at 

 first. Now, if any of the readers of 

 the Journal who are studying the 

 infusoria of other localities have any- 

 thing that will throw any light upon 

 the subject, I would be thankful for 

 the benefit of their experience. I 

 have looked through Carpenter's, 

 Kent's, and other smaller works, but 

 the subject is not mentioned, excejDt 

 the taking food particles through the 

 oral aperture brought there by the 

 action of the constantly- waving cilia. 

 Nothing is said about the stentor hav- 

 ing the povv^er of extending its proto- 

 plasm for the capture of larger prey. 



J. W. 

 Minneapolis, Minn. 



o 



Microscopical Techuic. 



II. MOUNTING IN GENERAL. 



Before describing the processes of 

 mounting, it is advisable to give a 

 brief account of the different methods 

 employed, and to offer a few sugges- 

 tions intended to aid the novice in 

 selecting the proper method for what- 

 ever specimen he may wish to pre- 

 serve. 



If any thin, transparent specimen, 

 such as a piece of feather, fibres of 

 cotton or wool, for exainple, be placed 

 under the microscope and examined 

 while dry, and portions be then ex- 

 amined successively in water, glyc- 

 erin, and spirits of turpentine, it will 

 be observed that the successive media 

 cause the fibres to appear clearer and 

 more transparent as we pass from one 

 to the other in the order named. On 

 seeking for the explanation of this 

 fact, it will be found that as the light- 

 refracting power of the liquid in- 

 creases, the objects immersed in it 

 seem to become more and more trans- 



parent. When we look at a trans- 

 parent object with the microscope, 

 throwing the light upon it and through 

 it from the mirror below in the usual 

 way, the visibility of the object is de- 

 termined by the refractive power of 

 the object, as compared with that of 

 the medium by w^hich it is surrounded. 

 When the difference in refractive 

 power is considerable the object is 

 distinctly seen. When the difference 

 is slight the object becomes almost 

 invisible. If a piece of glass be 

 plunged into a bottle of Canada bal- 

 sam, it becomes almost lost to sight, 

 because balsam and glass refract light 

 almost equally. In water it is some- 

 what more visible, but still not so 

 distinctly as in air. Advantage is 

 taken of these facts in movinting mi- 

 croscopic objects, and it will readily 

 be inferred that the appearance of an 

 object will depend greatly upon the 

 method of its preparation. 



Besides affecting the visibility of 

 an object, depending upon its refract- 

 ive power, the mounting medium 

 often affects the appearance of the 

 object in another way, by making it 

 more transparent. This it does by 

 filling up the pores and interstices 

 with a medium that is transparent 

 and of a refractive power somewhat 

 greater than air. A piece of thin 

 paper or a thin shaving of wood is 

 translucent, but water or oil "will 

 make either of them almost transpar- 

 ent. A longitudinal splinter of a 

 match cut as thin as possible with a 

 pen-knife is an excellent specimen to 

 experiment with to observe different 

 effects in mounting. If the splinter 

 be placed on a slip with water and a 

 thin cover-glass applied, it is jDrob- 

 able that the beauty of the specimen 

 will be greatly marred by numerous 

 minute circles with comparatively 

 thick and black borders distributed 

 here and there. In some places the 

 woody structui-e will be clear and 

 transparent ; in others it will be filled 

 with black lines, more or less discon- 

 tinuous. All the black portions are 

 caused by air, either in bubbles or 



