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MUSCULAR ACTION (VOLUNTARY AND INVOLUNTARY) 331
Similar remarks, but in a modified sense, apply to the involuntary hollow muscles, such as the heart, oesophagus,
stomach, rectum, bladder, uterus, &c.
In these there is a distinct double power of opening and closing, these movements being spontaneous and
independent of each other.
By ascribing to the sarcous elements of muscles, and the muscles themselves, a double power, namely, a
centrifugal and a centripetal power, whereby they can close, contract, and shorten on the one hand, and open, expand,
and elongate on the other, all the difficulties connected with muscular action are obviated. The subject is further
elucidated by regarding the closing or centripetal and the opening or centrifugal movements as both vital in their
nature, as we in this way get rid to a large extent of elasticity as a supposed prominent and necessary factor in
muscular movements. By investing the sarcous elements of muscles with the double power in question we assimilate
their movements to those witnessed in protoplasm, in white blood-corpuscles, in amoebee, pseudopodia, &c. We,
in fact, invest muscle with a certain degree of pushing or aggressive power which is fundamental in all vital move-
ments. Animals directly or indirectly advance and throw themselves upon their prey, and the centrifugal advancing
power is, in some senses, more important than the centripetal or retreating power. Even plants are aggressive as
far as the search for food is concerned. The roots, branches, and leaves continue to advance so long as plants
grow. Whenever advance and growth cease, and a condition of stasis sets in, the plant is on the high road to
decay. Plants, hke animals, possess a centrifugal and a centripetal power ; the former enabhng the plant to seize
the elements required for food, and the latter enabhng it to draw in the elements necessary as food into its interior,
where they are assimilated.
All cell growth and transformation are the result of atomic and molecular motion, and as cells reproduce
themselves endogenously, exogenously, fissiparously, and gemmiparously, the movements are at once extensive and
varied.
The elaboration of cells into tissues hkewise necessitates movements. Further, the various processes in plants
and in animals, such as digestion, assimilation, secretion, excretion, muscular and nerve action, &c., are the outcome
of movements. The Hving plant and animal, the simplest and the most complex, are fundamentally moving masses
of sentient protoplasm, and it is only by studying protoplasm and protoplasmic formations and movements that we
can hope to get a real insight into the economy of plants and animals in their entirety.
If we could peer into the interior of a plant or an animal, and our eyes were equal to the occasion, an unparal-
lelled scene of activity would meet our gaze ; gases, fluids, semi-solids, and solids all hurrying hither and thither in
the most complex and bewildering manner, yet all according to law and order. Indeed all the most wonderful,
if not the most beautiful, parts of plants and animals, are concealed by non-transparent tissues and integuments.
Electricians are sanguine enough to believe that at no very distant day a light, sufficiently powerful, will be
devised to make all living bodies diaphanous. Should that day ever come, biology and physiology will enter on
a new era. Then we shall see face to face, and not through a glass darkly, as at present. The discovery of Rontgen
rays is a step in the direction indicated, and already the bones can be photographed within the muscular cycles
which actuate them. By these means also foreign substances, which have gained surreptitious entrance into the
body, can be detected.
The movements of transparent living matter are of the utmost consequence in biology and physiology, and
this fact invests the study of transparent rudimentary plant and animal forms with ever-increasing interest.
The simplest plants known are the unicellular plants, of which the yeast and snow plants are examples. These
low rudimentary forms are perfect in their way. They live, grow, and reproduce themselves with as much certainty
as the higher forms. They are literally foci of force and movement.
Many of the spores of plants move, some by means of cilia, some by flagella, and some in virtue of their spiral
shape. It not unfrequently happens that the young of plants move freely about until they find a suitable habitat,
when they cast anchor, develop roots, and fix themselves. Similar remarks are to be made of animals—sponges, for
example. The sensitive and insectivorous plants, though fixed, are continuously in motion, and so of many fixed
animals.
Plants circulate their nutritious juices ; they respire ; they secrete and excrete ; they grow and reproduce
themselves ; they move in all their parts. Plants close and open their leaves and the stomata contained in the
leaves ; they are more active during the day than during the night, and in summer than in winter. The stem
grows in length and in breadth ; the roots shoot downwards and outwards ; the branches upwards and outwards ;
and the leaves in a great variety of directions. The stems, roots, branches, and leaves often move in a spiral
manner. They perform movements of gyration, circumnutation, &c.
The movements of animal protoplasm are, if possible, more interesting than those of vegetable protoplasm.
Some authors maintain that vegetable and animal protoplasm are not only similar but identical. This