GLOSSARY. 253 



Spherical Aberration. The errors of lenses arising from 

 the spherical surface, so that the rays from centre and 

 edge do not accurately combine in focus. 



Spontaneous Generation. The theory of the spontaneous 

 or independent origin of minute organisms. Bastian's 

 views in favor of this theory seem to have been over- 

 thrown by the experiments of Pastern and Tyndall, and 

 biologists now generally agree to the doctrine that all 

 living bodies are derived from pre-existent life. 



Torula. The " yeast-plant " fungus. 



Vernier. A short graduated scale, made to slide along 

 a large scale so as to read to fractions of divisions. 



Vibriones. Vibratile filaments, or bacteria, sometimes 

 moniliform, or bead-like, frequently found in decaying 

 animal infusions. 



Wandering Cells. Leucocytes, or 'white blood-cells, 

 which pass through the coats of vessels and thence into 

 neighboring tissues. 



