[It was a great honour for me to receive an invitation from the Senate of the University of London to speak on a psychological subject. I had, however, some diffidence about accepting it, since I have to speak in a foreign language. I feel greatly relieved by the assurance that there is to be no discussion after the lecture. Furthermore, I have brought some lantern-slides with me, to render my lecture more intelligible.]

When I was asked to either open a discussion or read a paper, I felt a great difficulty in choosing a subject, and I think my choice has been influenced considerably by the interest shown by the public in mental defect. Probably all of us are conversant with some of the various methods that are in use for testing the intelligence. These appear to resolve themselves into either valuing or “marking” by plus or minus or using numbers. It has always appeared to me that in marking by plus or minus signs it is very difficult to form an opinion as to whether it should be + ! or + ?, whereas it is easier to use figures. For instance, you say to a child, “What is the difference between an orange and a banana?” and you desire two comparisons to be given. If you give one mark for a definite comparison and no marks for an indefinite comparison it appears fairly simple, whereas if you are marking by the plus signs and one comparison is correct and the other wrong, it appears to me to be difficult to tell which of the plus signs one should use in marking the whole result. I therefore use the point scale test of Yerkes and Bridges. This method, with some slight modifications of my own, I and my colleagues have used in all the cases. I do not believe that a child cannot be tested until it has reached the age of five years. In this I have some support from recent American workers, and a method of testing the young child may yet be devised. Therefore in marking I do not, as Yerkes and Bridges do, start from five years of age, but as though the child could think from birth. The two tests which I hope to discuss at this meeting are those of association and suggestion. These two units appear to offer some interesting theories which might be worthy of further investigation. In a sense these two tests are dependent on each other psychologically and throw some light on the elucidation of some of our problems, and may perhaps enable us to form deductions of some diagnostic and prognostic value.

It is exactly forty years ago since Dr. Guye, of Amsterdam, drew the attention of the Section of Otology, at the annual meeting of the British Medical Association held in Leeds in 1889, to the presence of certain mental disabilities, designated aprosexia, which may appear, both after as well as before puberty, in the subjects of chronic nasal disease. I submit that mental symptoms additional to those described by Guye are due to diseased conditions of the nose which produce a persistent catarrh.

The ordinary method of making an emulsion of fæces in saline or broth and plating therefrom is of value in gross pathological infections of the bacillary and coccal variety. As a method of isolating the sum total of aerobic fæcal streptococci, it is, however, peculiarly incomplete. Anyone who cares to incubate a specimen of fæces in 1% neutral glucose broth and plate therefrom on successive days on to blood media will notice some very interesting facts. Whereas, in the majority of cases, coliform bacilli will grow therefrom in the first two or three daily platings, after a few days they cease to be recoverable and are replaced by streptococci of various types, sometimes later by staphylococci or moulds in pathological instances, and finally all that can be grown are Gram-positive bacilli or filaments. These bacilli are the lactic acid or acidophilus bacilli, and they have, by their production of acid and possibly by other lethal products, destroyed all aerobic bacilli except themselves. In time they, too, succumb, not apparently from hyperacidity, but from lack of pabulum. They can easily be kept alive by transplantation, to either human citrated blood-agar or glucose broth. Elsewhere∗ I am publishing a detailed account of this “acidophilus phenomenon,” but a consideration of the annexed Table I will make tolerably clear the mechanism of this curious process. It is, in the main, a question of acidity, inasmuch as any germ which produces a lower hydrogen-ion concentration (that is, a more acid medium) will inevitably destroy any accompanying germ which produces a less acid medium. For instance (see Table I), a mixture of B. coli communis and Staphylococcus aureus will eventually yield from glucose broth a pure culture of the latter organism, since B. coli produces a pH of not less than 4.0 in neutral glucose broth, whereas the staphylococcus can produce a pH of 3.8. Likewise a streptococcus producing a pH of 3.8 will oust a B. colt producing a pH of 4.2–4.0. We should thus expect an alkaline stool to yield a majority of coliform organisms, and a more acid stool to yield a majority of streptococci or staphylococci; this is precisely what happens.

Pyretotherapy, or the artificial induction of pyrexia as a means of treatment of the psychoses, has engaged the attention of psychiatrists for many years. The means employed to this end have been numerous, and they may be divided into two classes:

1. Chemical: Hypodermic injections of sodium nucleinate; or of protein in the form of peptone, blood, milk, tuberculin or emulsions of dead bacilli.

2. Infective: The introduction of living organisms, especially Plasmodium vivax malariæ and Spirochete recurrentis duuoni.

For the past three years at Claybury every case of general paralysis treated by malaria has received a course of injections of arsenic (sulfarsenol) concurrently with the routine course of quinine. During twelve months of this period the majority of cases were given, in addition, (a) a course of iodide and mercury by mouth, and (b) a course of intravenous injections of tryparsamide.

By the erythrocyte sedimentation phenomenon is meant the rate at which the red blood-corpuscles settle in an anti-coagulative column of blood. Numerous modifications of the method are in use, differing only in the way results are recorded and in minor details of technique.

The appointment, believed to be the first of its kind in this country, of a whole-time gynæcologist to a mental hospital,∗ marks a big step forward in the care of the mentally afflicted.

In previous communications I have shown that the excitation processes mediating mind are essentially due to an interaction between Ca salts and colloids; also that behind a response or thought of a particular size there can lie an infinite series of excitation processes differing in the proportions of the two interacting factors. This composition next determines the type, or quality, of thought.

Application of the previously given formula for mental excitation processes (z), viz., H + L = T, to the problem of pain indicates that L, the thing felt, is judged through H, and the two together produce the response T.

I assume that cutaneous pain is a special sensation with naked nerve-endings as its “receptors.”

In the present communication it is intended to consider the fundamental formula of mental excitation processes, H + L = T, in terms of seeing. The equation implies that the characters of a light stimulus L are judged through a second factor H. T is the response of the responding organ.