June 16, 1899.] 



SCIENCE. 



847 



order, a most interesting historical notice of the 

 first attempts to accurately estimate the visual 

 power, the invention of the ophthalmoscope 

 and the apparatus required for testing vision 

 opens the volume. This is followed by a com- 

 prehensive description of presbyopia, myopia 

 and hypermetropia. 



Astigmatism in its various forms is taken up 

 next, under which heading au extended account 

 of ophthalmometry to its minutest detail is 

 given. Asthenopia, particularly that which is 

 found in association with binocular vision, is 

 described in a graphic manner, while a number 

 of useful general remarks as to lenses, specta- 

 cles and eye-glasses finish the volume. 



A careful perusal of the contents of the work 

 is recommended to any one who may be inter- 

 ested in the subject. 



C. A. O. 



BOOKS EECEIVED. 



German Higher Schools ; The History, Organization and 

 3Iethods of Secondarij Education in Germany. jAMES 

 E. EussELU. New York, London and Bombay, 

 Longmans, Green & Co. 1899. Pp. xii + 455. 



Year-hook of the United States Department of Agriculture, 

 1899. Washington, Government Printing Office. 

 1899. Pp. 768. 



Imperial Democracy. David Stare Joedan". New 

 York, D. Appleton & Co. 1899. Pp. viii + 293. 

 $1.50. 



Eighteenth Annual Report of the United States Geological 

 Survey, 1896-97. Chaeles D. Walcott, Director. 

 Part II., Papers Chiefly of a Theoretical Nature. 

 Part IV., Hydrography. 'Washington, Govern- 

 ment Printing Office. 1899. 



SOCIETIES AND ACADEMIES. 

 THE BIOLOGICAL SOCIETY OF WASHINGTON. 



The 306th regular meeting was held April 

 8th. The first paper entitled ' The Ferns of 

 Hemlock Bluff' by Mr. Wm. Palmer included 

 a preliminary sketch of the geology of Hemlock 

 Bluff, a point on the Virginia shore of the 

 Potomac between Georgetown and Great Falls. 

 The locality is particularly rich in cryptogamic 

 plants, over twenty species of ferns being 

 enumerated. 



A recent noteworthy addition to this list is 

 that of Asplenium pinnatifidum hitherto un- 

 known from the District of Columbia or the 



adjacent parts, and supposed to be confined to 

 limestone rocks in mountain regions. The 

 rocks at Hemlock BluflP are, however, gneissic. 

 Mr. Palmer stated that this interesting and 

 beautiful station is threatened with destruction, 

 and expressed the hope that Congressional action 

 would be taken in time to protect the banks of 

 the Potomac from further devastation. 



' Notes on the Habits of African Termites ' 

 was the subject of the second paper, read by O. 

 F. Cook. On the basis of observations made in 

 Liberia several points in the domestic economy 

 of termites have been established. Among 

 these may be mentioned the fact that some ter- 

 mites regularly collect rotting wood, which 

 they put through a process of curing and then 

 comminute into the pulp used in building the 

 irregularly honeycombed fungus gardens which 

 produce the food of at least the young animals 

 of the colony. The soldiers of these species 

 {Termes helHcosus and allies), which sally out 

 from the nest in response to attacks by men or 

 animals, do not return to the nest, but wander 

 about and soon perish from exposure to the out- 

 side air. Other soldiers, the so-called nasuti, 

 of which the head is produced above into a long 

 beak, eject from this process, which is hollow, 

 a transparent, acrid, malodorous and corrosive 

 fluid, which forms a most effective means of 

 defence against ants and other insect enemies, 

 and renders them distasteful to birds. A third 

 type of soldier can neither shoot nor bite, but 

 the large, unequal mandibles are especially 

 adapted to produce a loud clicking sound 

 which furnishes protection at least against other 

 species of termites. It was also found that the 

 perfect insects associate in pairs when flying 

 over water and that, after dropping their wings, 

 such pairs are able to burrow into the ground, 

 thus suggesting the possible origin of termite 

 communities. 



Under the head of ' Biological Characteristics 

 as a means of Species Differentiation ' Dr. 

 Erwin F. Smith described in detail the very 

 numerous culture-methods, reactions and other 

 tests now in use in bacteriology. To accomplish 

 all these investigations a species is sometimes 

 carried in the laboratory for two years or 

 longer. The insuflSciency of the older and, 

 indeed, of many of the more recent descriptions 



