The Authors have studied the voices of twins by means of an intrageminal identification test. They have recorded the voices of 104 twin-pairs (58 MZ and 46 DZ), asking each twin to listen to the play-back of his own and his co-twin's voice, urging him to indicate which of the two voice samples was his co-twin's.

In 66% of the MZ pairs both twins were unable to identify their co-twin's voice; in 21% of the MZ pairs only one twin identified his co-twin's voice, and in 13% of the MZ pairs both twins could identify their co-twin's voice. In the case of the DZ pairs the corresponding results are completely reversed, as they are respectively 2%, 20% and 78%.

This experience shows that the voice of MZ twins carried over the air is concordant and practically identical in its acoustical effect. Furthermore, the comparison of this result with the one afforded by the voice of the DZ pairs proves that the mechanisms charged with originating the human voice are highly conditioned by heredity.

Among 520 sibships, in which at least one child was an epileptic and for which the family history and clinical findings were quite complete, there were 294 with one parent affected, 222 with neither parent, and 4 with both parents affected. Numerical tests on the pooled data show quite definitely that epilepsy is inherited as if due to a simple autosomal dominant gene with approximately 65% penetrance. Since about 65% of all epilepsy is genetic and since there is about 65 penetrance in genetic epilepsy, the 2 factors effectively balance one another, so that the incidence of epilepsy in the population, 1 in 200, may be taken as the frequency of individuals with a genetic constitution for epilepsy.

Assuming random mating, the gene frequency for the dominant gene for epilepsy is 0.0025 and for the normal recessive allele the value is 0.9975. It follows that only about 1 in 160,000 is homozygous for the dominant gene for epilepsy and that 99.5% of the population are genetically normal. For the genetic counselor it is of interest that if one parent has a genetic constitution for epilepsy the frequency among the children is about 36%, and if one child in such a family has epilepsy the empirical probability of another child having epilepsy is about in 1 in 8, which having regard to the standard error, agrees with the degree of concordance (10.3±1.8%) in dizygotic twins, as should be expected.

In estimating twin frequencies from birth and mortality data, it is necessary to make some statistical corrections, the extent of which is demonstrated for the general population of the United States. In this population, twins constitute 2.19 per cent of all babies born since 1928. This rate is reduced to about 1.9 per cent by excess twin mortality within the first year of life, while the 2:1 ratio of same-sex to opposite-sex pairs observed at birth remains virtually unchanged. Later mortality reduces the proportion of males, but not to such an extent — even at age 75 — as to necessitate modification of the 1:1 sex ratio in estimating the proportion of monozygotic pairs by Weinberg's differential method.

After the first year of life, there is no evidence for a significant difference between the mortality rates of twins and nontwins, so that the proportion of twin individuals in the population may be assumed to remain nearly the same at all ages. However, as pairs are broken by mortality and migration, the number of intact pairs is reduced at successive ages. Among people who survive to an advanced age, the relative frequency of pairs represented by at least one twin may be nearly twice as great as at birth. For comparative purposes, therefore, the most useful way to express twin data is in terms of individuals rather than in terms of twin pairs.

The statistics describing a twin sample should be computed from index cases (probands) rather than from twin pairs, if some or many pairs are represented by a single index case. Only then can the sample be compared with a larger population either in terms of twin frequency or in terms of proportions within the sample. The latter comparison might involve the proportions of opposite-sex and same-sex pairs, the proportions of monozygotic and dizygotic pairs, or the proportions of diagnostic subgroups. The same type of computation is also required for the estimation of penetrance and concordance rates. In the latter case, however, the number of index cases from concordant pairs should be halved in order to correct for the twofold representation of concordant pairs in the sample.

Report of 2 pedigrees during 4 and 3 generations respectively, whose members have been investigated by the author personally with the splitlamp. In addition to these pedigrees some more smaller families were examined and compared with communications from the literature. All this leads to the assumption that the lacunar type of irisstructure with its irregular and more peripherically situated irisfrill, as a result of increased reabsorption of the iridopupillary membrane, is an autosomal trait, which behaves like a single dominant. The iris with a more continuous boundery layer and an irisfrill which is situated nearer to the pupil is recessive. It will be necessary in future to settle the genetic background of the subtypes of both contrasttypes, mentioned above.

Among the postulates of the twin method the Author describes especially the fundamental one of comparability. Whenever one assumes that the differences between monozigotic twins are due only to heredity (this is the basis of the twin method), one postulates in fact that environmental influences are of equal importance and act in the woy to differentiate one from the other both monozygotic and dizygotic co-twins.

The comparison between the two types of twins implies the identity of environmental influences and a conception of heredity and environment as indépendant variants.

As far as the psychological environment is concerned, the Author faithfully reports works on twin-condition: psychologically environment is defined according to the structure of the pair, of the duty of each co-twin the pair, and thus: a) two identical twins never hare an exactly identical environment; b) the environment of identical twins is never the same as that of non-identical twins.

Concerning pre-birth and peribirth conditions, the Author reaches the same conclusions of non-comparability between monozigotic twins, dizygotic twins and control groups of non-twins: difference in lenght of pregnancy, in weight at birth, in the rate of stillbirth and new-born deaths, in the mother's age.

The Author concludes not for abandoning the twin-method but for a revision of the criteria, and for a change of perspective.

The failure of comparison and of mathematical analysis applied to the difference between heredity and environment is not. completely negative. It reveals the inadequacy of such criteria at least in the field of psychology, and leads to overcoming them. The psychological environment does not appear as a still picture, but rather as a situation defined by the inter-social and differential duties. Furthermore, heredity and environment are variants closely dependent on each other.

A study of fingers characteristics was made on 1387 school children.

1. Clinodactyly (5th finger) with an angle of inclination of 21.3 ±0.7 degrees, was found in 15.2% of the male and 8.06% of the female white children between the ages of 5 and 12. These represent the heterozygotes of the population, Cc, while the extreme form of clinodactyly, with an angle of inclination of over 30 degrees, most likely represents the homozygotes of the population, CC.

2. Curved index finger (2nd) occurs less frequently than clinodactyly (in 2.22% of the group studied).

3. Flexed little finger (5th) occurs least often, about 1 in 320.

4. Bilateral penetrance ratio has been defined. Clinodactyly has a bilateral penetrance ratio of 0.77 in males and 0.64 in females. The curved index finger has a bilateral penetrance ratio of approximately 0.75.

5. Clinodactyly also occurs in Negro children.

6. An instrument is described for measuring the angle of inclination of clinodacyly.

In the family on study the Madelung deformity has been transmitted trough three generations as a dominant monomerous sex controlled ereditary factor with minor expression in the male sex.

This is to be considered as the most frequent type of hereditary transmission of the deformity.

In a patient the authors observed the following association of anomalies: bilateral hydrophthalmos with microcornea pseudo-plana, a thick-set somatic pattern, a small lower yaw, arterial hypertension, diabetes, disseminated intracranial calcifications, electro-encephalographic disturbances and neurological pseudo-extrapyramidal lesion.

His brother shows the following association of anomalies: unilateral hydraphthalmos, a thick-set somatic pattern, a small lower jaw, arterial hypertension, diabetes, digitiform impressions on the RX of the skull and neurological pseudo-extrapyramidal lesions.

The mother and grandmother of these two patients both showed a trembling of head and limbs, even as diabetes; by this means a dominant and polyphenic hereditary transmission must be accepted.

The A. presents the case of two sisters, both affected by mixed juvenile diabetes: diabetes mellitus and diabetes insipidus.

Three of their brothers died of diabetes millitus.

After discussing different etiological hypotheses, the A. indicates the hereditary one as the most likely.

Probably, in the case of the two sisters, there was an association of two hereditary processes, independent of one another, but coexistent.