LITERARY NOTICES. 



555 



of amoebae, and the opening directions for 

 obtaining them will give a good idea of the 

 clearness, directness, and simplicity with 

 which the whole work is written : 



Amoebae are frequently to be found in abun- 

 dance in the superficial ooze which forms a thin 

 layer upon the bottom of Dearly every quiet 

 body of fresh water. The ooze may be collected 

 from a pond, stream, or ditch, by gently and 

 slowly skimming the bottom with a tin dipper 

 fastened to a long handle. In gathering the 

 ooze be careful to barely skim the surface, and 

 to avoid disturbing the black mud which usually 

 occurs just below the ooze. 



Transfer the material thus gathered to a col- 

 lecting - bottle, and gather ooze from several 

 bodies of water, preserving each specimen in a 

 separate bottle, for amoebae may be abundant in 

 one locality and almost absent in another. Pour 

 the ooze into shallow dirhes, such as soup- 

 plates or bakinsj-dishes, putting enough into 

 each dish to form a layer about an eighth of an 

 inch deep over the bottom. 



Place the dishes near the window, where 

 they will be well lighted without exposure to 

 the direct rays of the sun ; fill them with fresh 

 water, and allow them to stand undisturbed for 

 two or three days, in order to allow the amoebae 

 to creep out of the ooze and accumulate at its 

 surface. 



If a permanent supply of amoebae is desired, 

 each dish may be converted into a small aqua- 

 rium by the addition of a few floating water- 

 plants, such as " duck-weed," and -when covered 

 with a pane of glass, to exclude dust and pre- 

 vent excessive evaporation, may be kept in 

 eood order for several months by simply replac- 

 ing with fresh water the loss by evaporation. 



In a day or two a thin brownish-yellow film 

 will usually be visible over the whole or parts of 

 the surface of the ooze; and portions of this 

 film, almost entirely made up of microscopic 

 organisms which have crept to the surface, may 

 now be examined for amoebae, in the following 

 manner. 



It only remains to add that this work is 

 published at a very low price. Considering 

 its cost and elegance, we hardly know of 

 another so cheap a book. And, considering 

 that there is no other book at all like it to 

 serve the purposes of introductory study in 

 its field, it ought to be in wide demand by 

 the students of natural history. 



Essays' on the Floating Matter op the 

 Air, in Relation to Putrefaction and 

 Infection. With Illustrations. By 

 John Tyndall, F. R. S., M. D. D. Ap- 

 pleton & Co. Pp. 338. Price, $1.50. 



Some of the researches contained in this 



book have appeared in the pages of " The 



Popular Science Monthly," and nothing, 



therefore, need be said to our readers tha* 

 is merely commendatory of their interest. 

 The volume is the result of extended re- 

 searches into one of the obscurest of sub- 

 jects the nature, conditions, and influence 

 of the invisible microscopic life of the at- 

 mosphere. Any inquiry into the dust and 

 floating contents of the air, if thoroughly 

 pursued, leads to the more subtile question 

 of infinitesimal forms of life and their 

 germs as floating elements of the breathing 

 medium. Profound problems are here en- 

 countered : Are these germs spontaneously 

 originated, or are they subject to the laws 

 of propagation which govern all other grades 

 of life ? Again, are these germs the seeds 

 of disease which affect the higher forms of 

 life, and thus become of the highest mo- 

 ment to the physician and the hygienist ? 

 The import of the subject has been dis- 

 closed only within the last few years, and 

 depends upon the perfection of the micro- 

 scope, and the most refined researches into 

 the nature and effects of fermentation and 

 putrefaction. Many able men in different 

 countries have been working, with intense 

 assiduity, over different branches of this 

 momentous inquiry ; but it was on many 

 accounts fortunate that Professor Tyndall, 

 about a dozen years ago, saw its importance, 

 and brought all his resources to bear upon its 

 systematic investigation. That he has thrown 

 much more light upon the subject by his skill- 

 ful and extensive experiments, and that he 

 has made very important contributions to the 

 establishment of the germ theory of disease, 

 will not be questioned. But in still another 

 respect it is fortunate that he identified him- 

 self with its elucidation. By his rare power 

 of exposition, and his wonderful clearness of 

 statement, he has done more, perhaps, than 

 all other writers to impress the medical pro- 

 fession and the public both with the vital 

 importance of the subject and the advance 

 that has been made in the establishment of 

 its fundamental principles. His present 

 book embodies the main results of his origi- 

 nal work, and, what is more, it presents 

 them in so lucid and inviting a form that 

 all classes of readers will be equally pleased 

 and instructed by his views. 



There is, perhaps, in the whole field of 

 science no illustration more striking than 

 is here afforded of the fruitful practical 



