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of any expression is one more lesson for the neurons of the muscles to learn. We might go so far as to say that these special neurons recite their lessons by the permanent expression which they give to us. The sad man, the worried man, the happy man, the hopeful or discouraged man, each has his own telltale face muscles;

ABRAHAM LINCOLN AFTER FACE MUSCLES HAD BEEN TRAINED

and a good student of human.

nature learns to read these faces almost as easily as if they were the pages of a book spread out before him.

As might be expected, it is old rather than young faces that most easily betray their owners. I myself am old enough to know this from my own observation. I have seen a fair, smooth, child's face change little by little into the strong, courageous, unselfish face of a man who is ready and glad to do his duty whether he likes it or not. And I have seen another face, equally fair, equally smooth, and equally young, turn little by little into the dissatisfied, weak, and sneering face of a man who never serves any one but himself.

Without planning for anything of the sort, with no idea of what was happening to him, each of these men

[graphic]

has trained his neurons; and they tell the truth about him even when he might prefer to have them tell a

different story.

All this is not a matter of being handsome, or of being plain to look upon, but simply a matter of having neurons which have learned to tell the silent history of the feelings and the emotions which have controlled a human life.

It is evident, then, that every young face is shaping itself to the expression it will have later; and that the time is sure to come when the tale of our inner lives will be told by the outward expression of face and manner. When that time arrives we may long to hide the facts about the history of our emotions. But we shall find that we cannot cheat the neurons. Instead, the story which they have been trained to tell will proclaim the facts about us whenever and wherever we show ourselves. In this chapter we have laid bare four great laws of the neurons:

1. He who wishes to do any sort of muscular work easily and well, and so thoroughly that it cannot be forgotten, must, by diligent practice, put that special business in charge of its own set of unconscious neurons.

2. Neurons are often so quick and clever that they learn that which we would much rather they would not learn; and they proclaim the truth even when we wish them to hide it.

3. If we wish our neurons to declare that we are courageous, kind, and sincere, the only way to make them do it is by actually being courageous, kind, and sincere.

4. He who pretends to have desirable qualities when he really lacks them will find that, through the power of his neurons, in spite of his desire, he actually declares to those whom he meets that it is all mere pretense.

CHAPTER XIII

PHAGOCYTE AND ALCOHOL, OR FRIEND AND

FOE OF THE NEURON

Scientists have known for a long time that red blood corpuscles are the oxygen carriers of the body; but for years they came to no conclusion about the occupation of his busy companion, the white blood corpuscle, the phagocyte, "the devourer," as his name means in Greek. The mystery vanished, however, when Professor Metchnikoff, of the Pasteur Institute, Paris, turned his attention. to the subject.

1

He took a healthy frog, carefully pricked some cholera microbes under his skin, and with his microscope watched the fate which befell them. The whole affair was easy to follow, for white phagocytes now flocked to the spot from all sides; they crowded close; each seemed to choose its special victim, and, drawing closer yet, laid itself up beside the enemy, stretched itself out as an amoeba might do, and little by little wrapped itself about the doomed microbe.

1 All phagocytes are white blood corpuscles, but there are also white blood corpuscles that are not phagocytes.

The phagocyte is really nothing more than a tiny round speck of protoplasm-merely a single cell like the amoeba - but it captures its victims relentlessly. In vain the microbes tried to flee; their captors had surrounded them completely and held them firmly within their own bodies long enough to digest them. Instead of killing an enemy outright and throwing him aside, they rid themselves of him by swallowing him whole. Quickly hurrying to another, each phagocyte repeated the process, disposing of one microbe after another and growing larger with each captive.

SHAPES WHICH ONE PHAGO-
CYTE TOOK WITHIN A
FEW SECONDS

When intruding microbes were small enough for it Professor Metchnikoff saw the phagocyte "swallow them in shoals as a whale swallows herring." Whereas, if they

were too large for one to manage alone, several phagocytes would surround the same microbe and digest him in partnership.

In this connection it is interesting to know that a frog never dies of cholera. The reason is clear to us; frog phagocytes are so vigorous that they conquer cholera microbes before they have a chance to manufacture their deadly toxin and give cholera to the frogs. In the same direction Professor Metchnikoff

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