The Educational screen (c1922-c1956])

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October, 19)2 Page 229 gladly scud catalogues to interested teachers gratis. However, the teacher may very cheaply prepare lan- tern slides himself or herself and in many cases to suit his or her particular demands better than those to be purchased. The following non-commercial sources afford a very good assortment of material to choose from:' American Museum of Natural History, 77th St. and Central Park-, West, New York Gty, N. Y.: Buffalo Society of Natural Science-.. Buffalo, New York; Indiana University, Bloomington, Indiana; Iowa State College, Ames, Iowa: Mass. Dept. of Pub- lic Health. University Extension. State House, Boston. Massachusetts; United Fruit Company, 1 Federal Street. Boston, Massachusetts; United States Dept. of Agriculture. Washington, D. C, and University Ex- tension Division. University of Wisconsins, Madison, Wisconsin. There are. of course, main commercial companies specializing in supplying educational slides, such as Keystone View Company, )a>. G Muir, Williams. Browne and Earle, C. W. Briggs & Company, Spencer Lens Company, and others. Motion Picture Films This type of visual aid is excellent and can not he overemphasized. Its use will increase tremendously without doubt, as soon as more material becomes avail- able for the subject of Biology. The following com- panies supply excellent material of this type, and many of the films may he rented as well as purchased: Bell and Howell Company, Bray Products Company, Car- ter Cinema Producing Company, Eastman Teaching Films, Inc., National Motion Pictures Company, and Powers Pictures. The Source and Preparation of Living Cultures The source of this type of material, is of course, practically unlimited and my hope is to cover such parts or material as will be of value to the teacher in the average introductory courses of Botany and Zoology. For this work the teacher should collect his or her own material, and when possible take students along and show them the sources of the material and thus fix important and interesting parts of the subject in their minds. Every student should be taught how to collect material and to have a fair knowledge of the flora and fauna in his particular locality. The teacher should provide himself or herself with a copy of Ward and Whipple's "Fresh Water Biol- Ogy" i published by John Wiley and Pros.. Inc., Phila- delphia. Pa.), which is an excellent reference work to use in the identification of plants and animals com- monly found in fresh water. A copy of Cray's "Man- ual of Botany" is essential in identifying the higher plants (published by American Book Co., Boston). Ugae and Protozoans are very abundant in all streams, rivers, ponds, pools, etc., and the teacher should examine material from these places in nearby localities to obtain what he needs for his eotirse (in the nature of living material). Of course one can col- 'lis material in some of the pond water and it will keep very well for a day or two if it is going to be used within that time for micro-projection purposes or class room microscopic work. However, the best way is to start a small aquarium and then these materials may he grown and kept for several months or even indefinitely with proper attention and then the teach- er will have his material at any time desired without the necessity of a special field trip. I started a 13 gallon aquarium this last fall and had scores of species of organisms available for nearly live months. The aquarium should be kept in a light place if one wishes algae to thrive. For animal life (other than the microorganisms from the river), to keep the aquarium balanced. I used two goldfish and two small turtles, and for vegetable matter (other than the microorganisms). 1 used Elodea, Cabomba, Myri- ophyllum and Sagittaria plants. I f one does not wish to keep an aquarium the fol- lowing solutions may be used to advantage in keeping organisms in good condition for a week or two: Moore's Solution Ammonium Nitrate 0.5 Grams Potassium Phosphate 0.2 Crams Magnesium Sulphate 0.2 Crams Calcium Chloride 0.1 Grams Iron Sulphate a trace KHop's Solution Potassium Nitrate 1 (Irani Pot. Phosphate ( K L .HP0 4 ) 1 Gram Magnesium Sulphate 1 Gram Calcium Nitrate 3 Grams Chloride of Iron a trace Dissolve the first three items in 1 liter of distilled water. .Add the Calcium Nitrate (a white precipitate will lie formed). When a more dilute solution is made from this stock solution, the bottle must be shaken thoroughly in order that a proper amount of the precipitate may be included in the diluted solu- tion. The above formula makes a 0.6*7r solution and this is used where vegetative growth is desired, while a 0.27r solution is best for showing reproductive processes and rapid cell division. Most teachers desire at some time or other to grow their own culture of Amoeba, Paramoecium and Eu- glena and thus obtain excellent material for micro- projection and so I shall outline methods for grow- ing cultures of these microorganisms. Dr. J. A. Dawson in a paper in the American Nat- uralist, gives minute instructions for rearing amoeba. The following is a summary of his suggestions: 1. Colled a quantity of water and pond weeds from ponds or sluggish streams nearby. I We have found that lily pads and colonies of oscillaria growing in stagnant ponds are a prolific source of amoeba.) 2. Place about 30 to 40 cc. of the collected water i Concluded <>n page J.'l i