of the straight muscles are materially modified by the form of the orbit. A broad, flat face at once suggests to the oculist a hypermetropic eye. A narrow face, with prominent features, is more likely to be associated with a lengthened eyeball, and, if the bones of the face are quite unlike on different sides, there is a presumption of astigmatism. With many exceptions, these general rules afford a tolerable estimate of the conditions of the eyes; but with varying depths of the orbit there must also be varying lengths of muscles. In many families a want of equilibrium of muscles is as characteristic a feature as hypermetropia or astigmatism.

Thus in the family of case No. 91 of the table, at page 145, the patient had hypermetropia, and had also converging strabismus. She had one brother and three sisters, all of whom were cross-eyed. Oculists often meet with such instances. Hence, the muscular balance of the eyes as well as their refractive condition enters largely into the composition of family similitudes.

If, then, the eyes in certain families are, as facial features, generally too short, or if there is in the family a tendency to squint, even if the tendency is not manifest to the ordinary observer, there is imposed upon that family an inordinate task, either in accommodating the eyes for near points or in maintaining parallelism of the visual lines. While the subjects of such defects are in full vigor, or while the parts subjected to the unusual demand are used but moderately, there may result little or no inconvenience.

There is under these circumstances sufficient nervous energy to supply the ordinary draft upon the nervous system and to perform this extra task; but if other excessive calls upon the nervous energy are made and the surplus vigor is expended, the difficult task of adjustment or of accommodation can no longer be performed without manifestations of nervous exhaustion. Hence, so long as no assistance is rendered to these overtasked muscles, disease or nervous prostration arising from their disability is exceedingly chronic, and long periods of rest with tonic medicines are required in order that a sufficient amount of reserve energy may be acquired to perform their function and also the requirements of active life.

The same nervous irritation does not always react in the same manner. This is well shown in BrownSéquard's experiments in tickling. One subject laughs, another cries, a third has contortions of the limbs, and the fourth tetanic rigidity of the muscles.

In case of irritation from difficult accommodation from refractive anomalies or excitation from muscular insufficiencies, family characteristics, such as hypermetropia or insufficiency of the externi, for instance, react in various ways. One member of a family suffers from migraine, another from chorea, and a third from neurasthenia. Again, in one such family the neuropathic tendency consists in eyes of insufficient length, while in another family the tendency may originate in a want of equilibrium of muscles. Thus the various forms of features, when deviating from an ideal standard of anatomical perfection, may give

rise to a great variety of anomalous conditions of the eyes.

It is very generally supposed that nervous diseases prevail to a greater extent in our own times than formerly. Should this prove to be true, which is quite likely, it is interesting to consider, in connection with this supposed increase of nervous troubles, the fact that at the present time the eyes are pre-eminently the working organs of the body.

When the amount of voluntary effort of the muscles of accommodation and adjustment of the eyes demanded by the exigencies of modern civilization from all but the most unskilled class of laborers is considered, it must be seen that in this may be found an explanation of any increased tendency to nervous dis

eases.

In several hundred instances the history of diseases to which members of families have been subjected has been ascertained with as much accuracy as possible. In a certain proportion the history has been obtained through several generations, but, as it is in most cases impossible to obtain any history beyond immediate relatives, efforts were principally directed to obtain a record of the present condition of parents, brothers, and sisters, if living, and of the cause of death if not living.

It is unnecessary to occupy the space which would be required to exhibit all this research, and a table is appended to this essay in which is shown the results of the inquiry in one hundred cases which are consecutive with certain exceptions here explained.

The cases chosen are all cases in which a specified

form of nervous disease existed and from which the patient was seeking relief. All cases of simple myopia or cases in which the refractive error is less than 1 D, and all cases of simple muscular insufficiency have been rejected from the list.

Myopia is a variable condition, and may arise from other anomalous forms of refraction. Slight refractive errors may or may not be the expression of a family characteristic; and muscular insufficiencies may often result from refractive errors. Hence all these cases, in which the hereditary influence is questionable, are left out.

The list, then, contains consecutive cases of nervous diseases in which the family record has been ascertained, and in which refractive errors of 1 D or more, excluding cases of simple myopia, have been found.

The exclusion of muscular insufficiencies appears necessary, and yet unfortunate; for, while these conditions are often acquired they are also not unfrequently hereditary, as has been shown.

The list of cases consists of adults, the ages ranging from seventeen to sixty-four years, and the family record contains none but immediate relatives-parents, brothers, and sisters.

In order to avoid complications which might arise from including the diseases incident to childhood, and especially as there is often a want of knowledge on the part of those of whom inquiry is made as to the nature of disease from which infant brothers or sisters may have died, all children under the age of twelve years have been excluded from the family record.