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measure at least, not simply the result of steady and gradual rises and falls of temperature, differing slightly in degree in the two parts compared, due to regular alterations in the rate of calorific production alone, but that the furnaces, which we may suppose the parts to represent, are, in many cases at any rate, liable to sudden and decided interferences with their ordinary action, causing rapid and irregular exaltations and depressions of their powers, and this in each part independently of the other. Thus, it is evident that in the case of “C” and “d” given above, in order to furnish such relative percentages of those set forth, quick rises or falls of temperature of 0.2° C., at the least, must have occurred, every time equality ensued this difference having to be made up, and, of course, a still greatest deficit having to be supplied with each reversal of the position of higher temperature.

If the extreme limits of thermal range, beyond which no rise or fall can normally occur, be the same or nearly the same in the two parts compared, it follows, of course, that, in a united rise or fall of temperature in both parts, as these limits are approached the average degree of difference of temperature would naturally tend to diminish, until finally, when the bounds were reached, either equality would be present, or a minimum difference of temperature in favour of that particular part the extreme thermal limit of which had the highest absolute level. But even with the extreme limits nearly the same, and with a united rise or fall in the two parts towards a higher or lower general level, this rise or fall may be very unequal in the two parts at different periods, and thus not only may frequent shiftings of the position of higher temperature from one side to the other occur, but also all shades of difference of temperature may be found at different levels, according as the rate of rise or fall varies in the two parts independently of each other. Therefore, in the hypothetical case given on page 5, of a rise from 34° C. to 35.1° C., the uniform difference of temperature of 0:1° C., given for the sake of simplification, would not probably be maintained throughout; but although, as the general level rose the average difference might diminish, yet even almost to the extreme upper limit-supposing the rise

to pass decidedly above 35•1° C.-irregular variations might bring about as great differences as those found at the lower levels.

Such being a "general idea of the conditions under which the temperatures of two parts may alter so as to leave each part at certain times superior in temperature to the other, or again, at other times, both parts equal in temperature, let us see what the results of our investigations show with regard to the influence of the degree of absolute temperature of the head on the frequency of occurrence of superiority of temperature on a given side or of equality of temperature of the two sides.

In the present article the writer proposes to analyse the results of some 6000 observations bearing on the questions in hand. These observations are contained in four tables, constituting each a separate and distinct set of experiments. The experiments were made on three subjects, the mental and physical conditions of whom were thoroughly known to the experimenter, and under circumstances where all external influences likely to affect the results were under careful supervision.* The division of the results into the four tables is purely accidental, depending simply on the fact that the observations were made at different periods, each period corresponding to the contents of a table. Each table, therefore, represents an independent series of experiments covering the greater part of the different absolute temperatures which are found normally in the portion of the head examined.

The part of the head examined lies back of the external angular process, and is thus bounded :- Anteriorly, by the external angular process, the frontal process of the malar bone, and by a line drawn upward from the external angular process parallel to the general plane of the forehead; posteriorly, by a line drawn upward from the zygomatic process of the temporal bone parallel to the anterior boundary line, and at a distance from it of 37 mm. ; superiorly, by a hori. zontal line drawn on a level with the summit of the superciliary arch ; inferiorly, by the zygomatic processes of the

The writer has elsewhere laid much stress on the importance of this intimate knowledge of the subject of experiment, and of the physical surroundings in which such experiments are made,

malar and temporal bones. The tract thus marked off includes of the writer's abitrary subdivisions, the 5th district, 1st tier, anterior region, and the 1st district, 1st tier, middle region, and covers the “ frontal station ".of Broca, adopted also by Gray and by Marigliano and Seppilli.

In making the experiments, the absolute temperature of one side-usually the left side-was first obtained, sometimes with the thermometer, and sometimes with thermo-electric apparatus; the difference of temperature between the two sides was then taken, always using for this purpose thermoelectric apparatus, and this difference, added to or deducted from the absolute temperature first obtained, gave the absolute temperature of the second side. After a certain number of comparisons the absolute temperature of the first side was again tested, and the averages obtained from the several examinations taken to represent the results of that particular set of observations. The method of taking the absolute temperature by thermo-electric means, although open to objections obvious to those accustomed to such investigations, is yet, in experienced hands, on the whole more satisfactory in work like the present than the use of the thermometer; for the former method can be conducted rapidly and repeated frequently, while the latter requires a far greater length of time, during which no comparisons of the two sides can be made, and, moreover, by the covering up of the part by the appliances necessary to protect and keep in place the bulb of the thermometer, augments the temperature of the part.

It will be observed in the tables, that the number of observations belonging to each absolute temperature is either fifteen or some product of this number. The reason of this is as follows. The object of the investigations was to find, in the case of each absolute temperature, which of the three conditions, namely, superiority of the right side, superiority of the left side, or equality of the two sides, was most frequently present. Now, suppose an examination at a given time, with an absolute temperature of 34:5° C. (92-1° F.) on the left side, shows the right side to be the hotter by 0.1° C. (0:18° F.). Continuing to compare the two sides with thermo-piles, we might go on for half an hour or an hour, still finding the right side the warmer by an amount equal

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to, or a little more or less than, that first found; but the number of comparisons which could be made in the times specified might vary greatly at different periods and under different circumstances. A number of experimental conditions beyond the control of the experimenter influence the rapidity with which such observations can be made. time the experimenter might proceed at the rate of an observation every half minute, while at another time several minutes might be spent with no certain result, and yet no change might have occurred in the relative temperatures of the parts compared. It would be out of place and occupy too much space to deal here with these causes of interference, which have, moreover, been fully considered by the writer in the work alluded to; it suffices to say that, through them, the number of observations which can be made in a given time may be decidedly affected. While, therefore, in half an hour, on one occasion, with the absolute temperature 34:5° C. (92-1° F.), we might obtain sixty results in favour of the right side, in the same time, with the same temperature, on another occasion, the superiority being now on the left side, we might obtain but fifteen results in favour of the latter side. Now to say that, at the particular temperature in question, the percentages of times of occurrence of superiority of temperature of the right and left sides are respectively 80 and 20, as the above results would indicate, would be to commit an obvious error.

The method pursued in these investigations was :- After finding the absolute temperature of one side, to make fifteen careful comparisons of the two sides. If the results of these comparisons were uniformly in favour of a single side or of

quality, and if, in the former case, the differences of tem perature noted were pretty nearly the same, the results were set down as so many observations for that particular absolute temperature. Nothing more was recorded for the time, but the temperature was tested at short intervals to see if any change occurred either in the absolute temperature of the side first examined, or in the relative temperatures of the two sides. If the absolute temperature changed, of course a new series of observations were made, and fifteen results were recorded for this new temperature. The same course was pursued if the position of higher temperature changed sides, or if equality was substituted for superiority of a side, or, finally, if the difference of temperature between the two sides underwent any decided change. But if no change occurred in the space of three quarters of an hour, fifteen more results, taken from those meanwhile made, were added ; and so on until a change occurred. If, on the other hand, at the start, during the first fifteen observations, any decided change took place, such as, for example, a reversal of the position of higher temperature, the course adopted was governed by the number of observations already made. If only two or three of the fifteen observations had been made the results were ignored. If only the same number were wanting to make up the fifteen, the full complement was counted as made. If half, or about half, of the full number had been made, they were put aside to be used to the credit of the particular condition which they represented in some future set of observations in which the same absolute temperature existed, thus going to make up another complement of fifteen. As a rule, however, the entire fifteen observations were completed at one time without interruption.

We will now proceed to examine the tables.

Each table is divided into two parts. The first part comprises those cases in which the higher of the two temperatutes compared is 35o C. (95° F.), or above that point; and the second part comprises those cases in which the higher of the two temperatures compared is below 35° C. The first two columns consist of the absolute temperatures of the two sides; the figures of the third and fourth columns are the differences of temperature in favour of one side or the other as the case may be; the fifth column gives the number of observations, and the sixth column indicates whether the results are in favour of the right side, or of the left side, or of equality of the two sides.

The tables will be analysed in two principal ways :-First, by comparing the percentages of frequency of occurrence of the conditions of right and left superiority of temperature and of equality of temperature respectively, in the two parts into which each table is divided ; and, second, by comparing the average absolute temperatures of the three conditions.

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