248 GLOSSARY. 



from its focal point. A very wide angle of aperture only 

 allows distinct vision of what is exactly in focus, so that 

 when penetration is needed most, as in physiological work, 

 a smaller angle is better than one used for resolution of 

 diatoms and other minutiae. 



Aplanatic. Destitute of spherical aberration. 



Archeus. The term applied by Van Helmont to the 

 specific agent which, according to his theory, presided 

 over vital functions. 



Bacteria. Minute, transparent, rod-like bodies, some- 

 times jointed, and often exhibiting a vacillating motion. 

 It is probable that they are produced by the germs of 

 fungi in a solution of animal matter. 



Bathybius. A term given by Professor Huxley to the 

 slimy matter from the ocean bottom. Doubts have been 

 expressed as to its animal nature. 



Binocular (binus, two, and oculits, an eye). An ar- 

 rangement of a prism (Wenham's) and eye-pieces for 

 two eyes, so as to produce a stereoscopic effect with the 

 microscope. 



Biology (Gr. Bios, life, and logos, a discourse). The 

 study of living beings, including zoology and botany. 



Bioplasm. A term proposed for the elementary sub- 

 stance of organic bodies when actually alive, or living 

 protoplasm. 



Blastema. The fluid matter, or plasma, in which, ac- 

 cording to the theory of Schleiden and Schwann, nuclei 

 first make their appearance, and then organic cells. 



Brunonian Motion. The molecular movement of fine 

 particles suspended in fluid, first observed by Dr. R. 

 Brown in 1827. 



Calcification. The infiltration of animal tissues with 

 salts of lime. 



Cell. The elementary unit of organic structure. From 

 the time of Schleiden and Schwann (1838) the researches 

 of biologists have been greatly aided by the demonstra- 



