Page:Popular Science Monthly Volume 25.djvu/184

174 third stage, h$3$+m$2$+l; etc. Although I shall say very little later on of involvement of middle and lowest centers in cases of uniform dissolution, it is most important, especially with regard to clear notions on localization, to recognize that the order of dissolution is a compound order.

The next division is local dissolution. Obviously disease of a part of the nervous system could not be a reversal of the evolution of the whole; all that we can expect is a local reversal of evolution, that there should be loss in the order from voluntary toward automatic in what the part diseased represents. Repeating in effect what was said on uniform dissolution, it is only when dissolution occurs in all divisions of the highest centers that we can expect a reduction from the most voluntary of all toward the most automatic of all. Dissolution may be local in several senses. Disease may occur on any evolutionary level on one side, or on both sides; it may affect the sensory elements chiefly, or the motor elements chiefly. It must be particularly mentioned that there are local dissolutions of the highest centers. It will be granted that in every case of insanity the highest centers are morbidly affected. Since there are different kinds as well as degrees of insanity, for examples, general paralysis and melancholia, it follows, of necessity, that different divisions of the highest centers are morbidly affected in the two cases. Different kinds of insanity are different local dissolutions of the highest centers.

I now come to give examples of dissolution. I confess that I have selected cases which illustrate most definitely, not pretending to be able to show that all the diseases of which we have a large clinical knowledge exemplify the law of dissolution. However, I instance very common cases, or cases in which the pathology has been well worked out; they are cases dependent on disease at various levels from the bottom to the top of the central nervous system. Most of them are examples of local dissolution:

1. Starting at the bottom of the central nervous system, the first example is the commonest variety of progressive muscular atrophy. We see here that atrophy begins in the most voluntary limb, the arm; it affects first the most voluntary part of that limb, the hand, and first of all the most voluntary part of the hand; it then spreads to the trunk, in general to the more automatic parts. To speak of a lower level of evolution in this case is almost to state a barren truism. At a stage when the muscles of the hand only are wasted, there is atrophy of the first or second dorsal anterior horn; the lower level of evolution is made up of the higher anterior horns for muscles of the arm. This statement, however, is worth making, for it shows clearly that by higher and lower is meant anatomico-physiologically higher or lower.

2. Going a stage higher we come to hemiplegia, owing to destruction of part of a plexus in the mid-region of the brain. Choosing the