# Page:Popular Science Monthly Volume 2.djvu/100

circumstances, but pretty uniform in the same solution. They are in length from ${\displaystyle {\tfrac {1}{15000}}}$ to ${\displaystyle {\tfrac {1}{2000}}}$ of an inch, and in thickness from ${\displaystyle {\tfrac {1}{30000}}}$ to ${\displaystyle {\tfrac {1}{40000}}}$ of an inch. The rods are formed of a series of granules placed end to end, and their appearance has been likened to a number of fine needles embedded in a thin film of glue. They often present a joint or line in the middle, dividing them into two equal parts. "Their movements are frequently of a more or less rapid, oscillating, or irregularly rotating character; though at other times they may be seen darting from place to place, either directly or in curves of various descriptions. All gradations exist, in fact, between movements which suffice at once to stamp them as living things, and mere slow oscillations, the presence of which alone may make us doubtful as to whether we have to do with living or dead organisms."
Along with the plastide-particles and the bacteria, there appears one of the lowest and simplest of organic bodies—the Torula, or yeast-plant (Fig. 1, C). The torula is a simple cell, possessing a cell-wall formed of a thin, homogeneous membrane, and containing a soft formative layer composed of protoplasm. These cells are about ${\displaystyle {\tfrac {1}{6000}}}$ of an inch and smaller, and multiply by budding or gemmation, being usually seen in chains, or clustered groups. Vibriones (Fig. 1, D) are described as jointed bodies, composed of long, rod-like segments, bent at various angles, which exhibit certain slow movements either as mere bending of the body, or else an actual undulating progression. In size they may vary from that of the largest bacteria, up to a body ${\displaystyle {\tfrac {1}{300}}}$ of an inch in length, by ${\displaystyle {\tfrac {1}{17000}}}$ in breadth, though there is no definite limit to their dimensions. The Spirilla (Fig. 1, E) are less common organic forms, characterized by the most active movements, and in which the body is thread-like, though twisted into the form of a helix, or spiral. Leptothrix (Fig. 1 F) is a name applied to certain filamentous objects that are generally motionless, and often not much thicker than vibriones. They may be either straight or undulating in outline, and perfectly plain, or marked by minute segmentations, after the fashion of the larger fungous filaments, into which it is said they sometimes develop.