Law of Avalanche.—How great is the power of the nervous system or the energy of it that may be set loose by some very simple reflex, as suggested by Forel, is illustrated by what Ramon y Cajal calls the Law of Avalanche. A single peripheral nerve ending is represented in many different portions of the brain. An ocular nerve ending, for instance, probably has direct connection with four or more portions of each hemisphere. Each of these portions of the brain has association fibers connecting it with other parts and so the stirring of a single nerve ending may disturb many thousands, perhaps hundreds of thousands, of brain cells; at least it affects them in some way or other. The older psychologists used to insist on the similarity, or analogy, between the cosmos ol the universe and the microcosmos that man is. The English poet of the nineteenth century told us that there is no moving of a flower without the stirring of a star, so intimately connected by the laws of gravitation is the universe. In the microcosm something of this same thing is true and a titillation of even the most trivial nerve ending may produce, in Ramon y Cajal's phrase, "an avalanche" of cell disturbances in the central nervous system which may seriously disturb the whole system.
What is thus true for the brain is true, also, for the cord, and the complexity of spinal cells needs to be seen to be properly realized.
Fig. 4.—SERIES OF SECTIONS SHOWING THE FINE NERVE ENDINGS AND BRANCHINGS OF THE FIRST AND SECOND LAYER OF THE VISUAL CORTEX OF A CHILD FIFTEEN DAYS OLD. A and B, very thick nerve plexus of the layer in which the little pyramids are contained; C, a plexus containing a series of branches that is less thick and intricate; D, small cells whose ascending axis-cylinders have resolved themselves into a set of similar branches; E, arachnoid star cells whose axis cylinders produce a thick plexus in the first layer; F and G, small cells with short axis cylinders that have very few branches. (Ramon y Cajal.)
Psychic States.—There are a number of human states representing extremes of sensory and intellectual conditions in man, that have always attracted attention, and in recent years have been special objects of investigation by physiologists. Natural sleep is one of these; the unconsciousness of narcotism or anesthesia is another. Hypnotism is allied to both of these, and would seem to lie on a plane between them. Then there are various states of exaltation in which sensations fail to produce their usual effect. Those [{112}] escaping from a fire, or passing through a severe panic of any kind may sustain all manner of injuries without being aware of them. Martyrs, for all manner of causes, are able to withstand suffering with such equanimity, and sometimes even joy, that it is evident that they cannot feel, as would people under ordinary conditions, the pain that is being inflicted on them.
Fig. 5.—FIRST, SECOND AND THIRD LAYER OF THE ANTERIOR CENTRAL CONVOLUTION (THAT IS, OF THE ASCENDING FRONTAL CONVOLUTION) OF THE BRAIN OF A CHILD ONE MONTH OLD. A, B, and C, little pyramids; D and E, medium-sized pyramids; F, cells with two sets of tufts; their axis cylinders resolved into end tufts; G, protoplasmic layer that comes from one of the large pyramids of the fourth layer; H and I, fine dentrites of the cells of the sixth and seventh layer; J, small cells with two end tufts; K, spindle cells with long axis cylinder. (Raymon y Cajal.)
FIG. 6.—LAYERS OF THE POSTERIOR CENTRAL OR ASCENDING PARIETAL CONVOLUTION OF A NEWBORN CHILD. 1. plexiform layer; 2. small pyramids; 3. medium-sized pyramids; 4. external large pyramids; 5. small pyramids and star shaped cells; 6, deep layer of large pyramids; 7, spindle and triangular shaped cells. (Raymon y Cajal.)
In the midst of intense mental preoccupation one may hold so cramped a position as would be quite impossible for the same length of time with the faculties normally engaged. There are pathological conditions, like hysteria, in which the pain and fatigue sense may, for a time at least, be quite in abeyance.