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seems rather plausible as a theory in view of the fact that low temperature goes to some extent with low intellectual power, for in that case there might be less blood going to the head in the case of idiots than with ordinary people and consequently the temperature, though lower there, might, in other parts of the body, be more on a par with that of people in general.

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On the other hand, these very low temperatures may be accounted for by the fact that the children may not have held the thermometer down closely against the tongue, but simply held it under the tongue rather loosely, or they may not have kept their

mouths shut tightly. I simply offer these as suggestions; so far as I know, the temperature was taken as it should have been.

The lack of correlation between pulse and temperature is rather surprising in view of the fact that physicians usually consider a rapid pulse as indicative of high temperature. This does not seem to hold here, for the pulse rate of the idiots was about that of people in general, 49 per cent. having reached the median of children in general, but the average for temperature was considerably below the median for other people. Of course the reason that they have been so correlated in people's minds is probably because both high temperature and rapid pulse occur in fever, but the connection between them is evidently not so close as has been supposed."

§ 13. Results Bearing on the Continuity of the Species My second conclusion was that idiots seem not to form a special class or species, at least as far as intellectual traits are concerned, but that they are included as part of a large distribution. I use the terms 'special class' and 'separate species' in the same sense as writers on this subject in general have used them. A group of individuals forming a separate species in any trait would be a group clustering about a certain central point and lying in the main outside the distribution of ordinary individuals in that trait. Its cases would in the main lie over 5 P. E. distant from the median for ordinary people. Here then we have two factors concerned in the determination of a 'species'-form of distribution and spread of distribution. Considering the second factor first, Figs. 20, 21, 22 and, 23, which show the distribution for those tests which we are inclined to designate as most closely connected with intelligence, do not fulfill the requirements of 'special species' from the standpoint of spread. In every test the cases run up to the median for ordinary children, and from Table XXXIII. (page 68) we see that more than 15 per cent. of the cases are included within the limits of normal distribution. Fig. 24, which is a composite of the four intelligence tests and shows the distribution of their averages for each child, illustrates the same fact.1

1 In making this average those cases of F were not considered at all, but only the tests in which the child had a grade of some kind were taken into account. This method was always followed in making an average. It would be interesting to know if the results would be the same had the F's been weighted. Of course, there are two possibilities in the weighting-to give the F a weight equal to the average of the grades received by that child in the other measurements, or to give the F a grade below the lowest grade received by any one in that test. This, however, has not been done as yet.

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FIG. 24.

Intelligence Tests.

Composite of Tests 6 AI, 6 A II, 6 B and 6 C.

FIG. 25. Memory Tests. Composite of Tests 14 and 3.
FIG. 26. Maturity Tests.

Composite of Tests 13, 12 and 4.

The grouping of any set of measurements always tends to throw emphasis on the norm and to eliminate individual variations, and that is what has happened in this case, and the conclusion can only be as stated that, overlapping the normal distribution as it does, this distribution can not be that of a special species. Figs. 14, 15, 16 and 17, which show the results of the individual dictations given in

test 14, Fig. 18, which shows these records combined, and Fig. 19, which shows the results of the test of memory of related words, all indicate that, from the standpoint of memory, there is no evidence of a special species. In some of the measurements the cases run as high as two and three times the P. E. above the median, and even higher in a few instances, while even in Fig. 25, which is the composite for the memory tests, the cases run a little above the central tendency of ordinary people. The results of the tests which I consider to be tests of maturity chiefly, point to the same conclusion. This is shown by Figs. 10, 11, 12, 13 and 26. The 'spread' of these surfaces and their overlapping of the corresponding surfaces for ordinary children then prove that there can be no separate species of idiots, at least in the traits examined.

Looking at the question from the standpoint of the form of distribution, we must arrive at the same answer. Going back to Figs. 20, 21, 22, 23 and 24, which show the distribution for the intelligence tests, no separate class or species could be represented by such surfaces as these. They show themselves plainly to be fag-ends of some larger curve. Of course the existence of such a large number of individuals who failed to do anything with these tests may be emphasized as a point against the conclusion on the ground that their presence in the surface might have changed its character. This objection will not hold, however, for such cases occur rather frequently among ordinary children and it has been found that when, upon a second trial, they have been made to understand the requirements, their records are scattered over a long distance on the scale, being in general low. Therefore, in this case we may presume that had the idiots understood what was wanted, their records would have been scattered over the lower part of the present distribution and hence not have materially affected the form of the surface. The surfaces showing the results of the memory tests, Figs. 14, 15, 16, 17, 18, 19 and 25, also show the absence of special grouping which would imply the existence of a species. The massing at the upper end of the surface is not so evident here as it was in the intelligence tests, but still there is nothing to point to the presence of a separate species. Glancing at the Figs. 10, 11, 12, 13 and 26, which show the results of the maturity tests, one might at first think that the form at least was indicative of a species. There is something that looks like a central tendency at a point three times the P. E. below the zero point. Still the fact that this point itself falls within the limits of the normal surface of distribution and the further fact that the cases spread down to 8 P. E. make the existence of a special species extremely doubtful.

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I made one other combination of results which in itself is practically valueless but which, taken in the light of the individual measurements shown, is of interest. Fig. 27 represents a composite of all the marks gained by each individual, save the physical measurements -height, weight, temperature and pulse. It contains more cases

FIG. 27

180 150 120

90 60

30

FIG. 27. Total. Composite of All Mental Tests.

than many of the other surfaces, for there were very few children who failed in every test right through. Of course the traits tested were so different that an average of all the results as expressed in such a curve is of little value. But it does show that so far as such a composite measure is valid, the defectives are not a separate species in the composite any more than they are in definite particular traits.

The question now comes up, "If these idiots do not form a special class, have we a right to say that they form the extreme of the ordinary surface of distribution." This is the view that has been supported by Galton, Ireland and Thorndike, although there seems to be no definite evidence. The fact already mentioned that the curves showing the distribution of idiots in the various measurements overlap the curves showing the distributions of ordinary ability, sometimes to such an extent that the upper limit is above the median, is strong evidence in support of the theory. In order to make the argument stronger, in the total mark for intelligence, memory and maturity, I separated the defectives found in the public school from those found in the institutions. Figs. 28, 29 and 30 show the results, the dotted lines representing the public school defectives and

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