It is noteworthy that a classification of men tal diseases based on their relation to physical factors is not satisfactory, for the reason that the disturbances in mentality are not always found associated with lesion or degeneration of any or all parts of the brain and nervous sys tem. In other words, a brain and nervous system which to all tests now applicable proves perfect in every respect may be found in the case of a person whose reactions to environ ment have been so unsatisfactory in adaptabil ity that he has not been able to act his part in society, which has had either to support him as an otherwise harmless dependent or con fine him as a destructive element. From this point of view the modern attitude toward men tal disease is that it is a regression, whether from physical or psychical causes, to the con dition of a more infantile or a more archaic type of mentality. It is recognized that the actions of the child resemble those of an earlier grade of human society, such as was the maxi mum of development in prehistoric ages; furthermore, that the responses of the modern individual to an environment which is daily becoming more and more complex are demand ing of the individual a much more delicate ad justment and adaptation. Whether the failure to adapt is caused solely by a physical lack in the make-up of the cerebral and neural con stitution is beyond the present power of physi ology and histology to determine. It is there fore quite as useful to classify mental diseases purely from the mental standard, providing, however, the already ascertained connections between certain types of reaction and the dis coverable lesions in the neural substance be not ignored. Therefore the present tendency in neurology is to make an analysis upon a purely psychical basis, namely, the mental mechanisms (q.v.) which have been observed to obtain both in the unconscious and in conscious life. It is now known that a phobia, or sudden un reasonable and excessive fear of some definite thing such as snakes, thunderstorms, knives, dogs, horses or what not, is neither to be ex plained on any conscious basis nor to be re _ .
moved by an appeal to reason or to conscious ness alone. Similarly the habits of mind named obsessions or compulsions are amenable neither to drugs nor to the conscious adjurations to forget them or avoid them, but only to the education of the character through the freeing of the fixated libido.
every alienist of re pute has attempted a classification of the forms of insanity. The subject is one of peculiar dif ficulty, owing largely to the fact that our inti mate knowledge of many of these various forms is far from complete.
A scheme of classification adopted by Jelliffe and White regards the diseases of the nervous system as falling into three general classes: (1) Those of the physico-chemical systems, affecting the neurology of metabolism, and ex pressed in visceral neuropathology and diseases of the glands with internal secretions; (2) those of the sensory-motor systems, including affections of the cranial nerves, the peripheral neurons, the spinal cord, medulla, cerebrum and cerebellum and the meninges, with syphilis of the nervous system, and (3) those of the psychical or symbolic systems (neuroses, psy choneuroses and psychoses). The last contains the manic-depressive group, the paranoia group, epilepsy, dementia precox, exhaustion and toxic psychoses and those associated with organic diseases, with senility, arteriosclerosis, and finally idiocy, imbecility and feeble-mindedness.
A more detailed elaboration of this ap pears as the 1918 classification of the American Medico-Psychological Association. The meth ods of examination of the nervous system in clude a questionnaire covering the family his tory of the patient and his illnesses, and an elaborate physical examination of the vegeta tive nervous system, of the sensory and motor systems, followed by a thorough mental ex amination which in many respects is somewhat similar to the questions of the "intelligence tests) and qualification tests of the army. The alienist comes in contact with a great many diseases whose mental element is very small, no greater in fact than that of the so-called physical diseases. The disorders in the physico chemical systems produce diseases with mental aspects, but aspects no more mental than those of the diseases affecting the organs, muscles, glands, etc., to which those nerves go. It is only when we come to what are called the neu roses that we 'find mental behavior alone or predominantly disordered. These affections were called neuroses or "nerve troubles) on the supposition once accepted that the mental behavior was caused exclusively by some pe culiarity, whether called abnormality, or merely variation, in the structure of the nerve cells themselves. At the present time, however, sci entific thought tends toward the theory that mental disease is determined by the loss of balance between the organism and its physical and psychical environment. Thus there are nervous systems congenitally so weak that they are practically disintegrated by the conflict of the individual and society, a conflict which is, as often as not, absolutely unconscious, and which occurs in the simplest and least com plicated social environment. In such natures mental disease at once appears because of the individual's inability to adapt himself to the rudimentary requirements imposed upon him from without. On the other hand, there are neural constitutions so strong or elastic that they are equal to a very severe strain of adaptation even to extraordinarily complicated environment. Such constitutions will naturally adapt themselves, retaining their own personal equilibrium and health, to conditions which would completely upset a weaker (that is, less adaptable) constitution. It may be here noted that the European War brought out many such diversities of neural constitution in those sub ject to "shell shock) or other war psychoses, together with improved methods of testing for congenital neural weakness. These tests have resulted in putting in positions of less nervous strain those who are unable to stand the greater. A similar allotment of individuals to the various tasks of life would naturally result in less nervous disease. For it is evident, when both factors are taken into consideration, the constitutional factor and that supplied by the environment, that mental disease is largely a matter of proportion between the nervous sys tem and the load which is placed upon it. For example, a person who is not obliged to strug gle for existence may never develop a mental disease which he would have developed, had he been subjected to the stress of adverse circum stances, while, on the other hand, his affluence may make him introversional, and, after the age of puberty, cause him rapidly to run counter to the demands of a true social exist ence.