218 APPENDIX. 



The general strncture sliould be carefully studied, the con- 

 tractile vacuoles particularly examined (they are seen best in dying 

 specimens or in those paralyzed by chloral), and dividing or con- 

 jugating individuals looked for (they are often abimdant). The 

 only really difficult point is the nucleus, which cannot be well 

 seen in the living animal. It may be clearly seen by mounting 

 a drop, to which a little dihite iodine or 2^ acetic acid has been 

 added. The former shows the cilia well, the latter the tricho- 

 cysts. Osmic acid and corrosive sublimate also give good preser- 

 vation. The internal changes during fission and conjugation 

 must be studied in prepared specimens mounted in balsam. Such 

 preparations are often of great beauty and interest. 



Vorticella must be sought for on duck-weed or other plants, 

 or on floating sticks, and the like. Zodthamnion^ Carchesium, 

 etc. , are liable to appear at any time in the aquaria. All these 

 forms are easily studied. Conjugation is very rarely seen, but 

 fission and motile forms are common. The macronucleus is 

 especially well shown in dead or dying specimens. 



Chapter XI Y. (Pkotococcus.) 



Protococcus {PleurocoGGus) is found in abundance on the 

 northerly side of old trees in many parts of the United States. 

 In case it cannot be obtained in any region it may be procured, 

 during 1895 and 1896, from Prof. Sedgwick, Institute of 

 Technology, Boston, Mass. , by mail. The laboratory- work with 

 it is too easy to require comment. See, however, Arthur, 

 Barnes & Coulter's "Plant Dissection" (Henry Holt & Co., 

 ISTew York). 



Chapter XY. (Yeast.) 



Bakers', brewers', compressed, and dried yeast may be had 

 in the markets. Brewers' yeast is to be preferred, as com- 

 pressed yeast-cakes contain starch, bacteria, and other extraneous 

 matters. All of the kinds may be cultivated to good advantage 

 in wort (to be obtained at breweries) or in Pasteur's fluids. (See 

 Huxley and Martin, chapter on Yeast.) Wild yeasts may be 



