86 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”carmine (a pigmented substance) was continuously poured toward the
oral cavity of a stentor. Following an initial period of indifference, the
stentor first bends its body to avoid the particles. When this response
fails to remove the undesirable stimulus, the stentor abruptly reverses
the beat of the cilia in an attempt to propel the particles away. If the stim-
ulus persists, the stentor suddenly contracts, and then slowly resumes
its normal shape. After about fifteen minutes of such contraction and
relaxation cycles, and in the continuing presence of the noxious particles,
the stentor violently sets itself free from the adhered surface and swims
to a new location. On landing, the stentor first explores the new surface
by crawling with the mouth touching the surface. Once a suitable spot
is found, it secretes a gelatinous material to firmly glue itself to the new
surface. This repertoire of behavior was observed repeatedly in many
individuals, with only minor variations.
Note that this is not a series of rigid, stereotyped behaviors started
off by a given stimulus. The organism expresses a goal to eliminate the
unwelcome change in environment by using various responses, ranging
from the mildest to the most drastic measure. Once the goal is achieved,
the stentor will go no further. It is only when one trick fails to remove the
noxious stimulus that the organism attempts the next stronger response,
ending with detachment from the site and swimming away to a new
location. That the stentor exerts an apparent “attempt” to overcome the
obstacle is obvious to the observer.
The sequence of responses can be interpreted in more detail as fol-
lows. First, the stimulus (carmine particles), though not causing imme-
diate injury, must be perceived as annoying and in the long run harm-
ful, and therefore should be avoided or removed. The reactions are of a
graded nature, from the most effortless to the most forceful. At first, the
stentor ignores the annoyance by continuing its normal activity. Then a
slight effort is exerted by turning the mouth away, while still engaged
in feeding. When this is ineffective in avoiding the stimulus, the feed-
ing stops temporarily and the ciliary current is reversed to get rid of
the particles. If this attempt still fails, the normal activity is completely