Even that much remembering, however, the tentacle-brain does not do especially well. After the animal has learned his paper-meat lesson thoroly one day, and can tell the difference straight off every time, the next day he has as thoroly forgotten it. If he learns it once more on the second day, he will as completely have unlearned it again on the third, and will swallow paper and meat with equal zest.

So much then for animals who do their thinking in rings instead of in spots. Now we shall see what happens to a creature who tries to do his thinking all over his body.

I have already mentioned the infusoria which swarm by the thousands in the water of ditches and puddles. They are decidedly small animals, the largest of them no bigger than a pin head; and as I explained before, they are remarkable in that each infusorian is just one single cell. Most of them are free-swimming, that is, they go about as they like thru the water as a fish does; but some grow on stalks like flowers, tho even these can usually let go their anchorage and float away to a new station.

[ More common infusorians, much enlarged. ]

Small as they are, they feed on still smaller plants, the bacteria. Nevertheless, they do not know their food either by sight, hearing, taste, or smell. One hungry infusorian, looking about in search of his dinner, will pass right by a mass of bacteria large enough to feed him the rest of his life and not notice it. He will swim so close as almost to graze the feeding ground, yet keep straight along without turning or pausing, as if it were not there. The next instant, he may run against some small particle which isn’t good to eat at all, and swallow it down forthwith. In fact, the infusorian simply swallows whatever happens to hit his mouth. If this happens to be good to eat, why so much the better. If it happens to be only a grain of dust or a fleck of shell, down it goes just the same; the infusorian doesn’t know the difference.

When the infusorian, swimming straight ahead, runs into some obstacle too large to swallow, it stops, backs off, turns a little to one side, and goes ahead again. But he never takes any pains to turn toward the side which will do the most good, or to notice whether he turns enough to do any good at all. He is just as likely, having run against the extreme end of some object, to turn exactly the wrong way, so that he hits it next time fairly in the middle. Then he backs off once more, turns again, and swims ahead. Perhaps this takes him by; perhaps he butts the obstruction again at the spot where he struck it first. Then he tries again, and yet again, and in the course of time, usually manages to get by.

So the infusorian is a funny little machine, made so that when it hits anything it backs off, turns somewhat, and goes ahead again. If one is very clever with his fingers, as men who study creatures such as these have to be, one can take a slender needle and touch the infusorian on the front end—we cannot call it the head. Thereupon he stops, backs, turns, and goes ahead. Touch him on his side. Again he stops backs, turns, and goes ahead. Prick him from behind. Once more, he stops, backs—right on to the needle which is pricking him—turns, and goes ahead. Try heating the water. As soon as the infusorian feels uncomfortably warm, he stops, backs, turns, goes ahead. Try cooling it. The same process. Add to the water something that the creature notices, acid for example. Still the same old stop, back, turn, go ahead; tho often the next go-ahead sends him straight into the drop of acid and burns him up.

So far as we can see, therefore, everything that the infusorian feels at all, feels to him exactly like everything else. No matter what it is he feels, nor on what part of his body he feels it, he always acts in precisely the same way. It is, moreover, doubtful whether one of these animals ever learns or remembers much of anything, or in any other way ever finds out how to do anything which he could not do about as well the first instant of his life.