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.

In a lecture to a group of physicians of sporting societies the Author presents the phenomenon of the family habit of sporting practice as the signo of the existence of a hereditary basis for sporting proficiency.

Referring to research by other Authors, and especially by Grebe, the Author relates the most significant case histories of family sporting practice afforded by Italian sports.

The hereditary transmission probably takes place through a mechanism of dominance; the Author suggests the method which can be employed in order to enact a genetical study of sports and of athletics.

Drawing is an excellent means of investigating the personality of identical twins. It gives an overt expression of the difficulty of arriving at the consciouness of the self, so frequently found with these persons. Some of this article's drawings illustrate this fact and show the persistence of duality and confusion.

The strength of the tie to the other twin, the wish for indépendance from him, the dominance of one subject in the pair are also made manifest.

Furthermore, the existence of some affective reactions toward the family and the frequent opposition between the types of behavior, found in the two members of a same pair toward the auter world, are shown.

The report explains how twin-studies may affect the science of population, both directly by their frequency and determining factors, and indirecdy in as much as twins provide a useful research method to study the physical and psychological traits which identify a human population.

It is possible, in fact, through the method of intrageminal-in-tergeminal comparison and through other methods, to study the population's normal and pathological traits.

As far as diseases are concerned the twin method affords the chance to discover or to reassert the hereditary nature of many diseases as well as the hereditary aspects of morbid receptivity and reactivity in the esogenous diseases; furthermore, it is possible to probe deeper while studying hereditary diseases especially in the fields of phenogenesis, variability and nosological classification.

The study of psychological traits in twins makes it possible to identify the instinctive tendencies and the hereditary components of the mental functions; also the study of learning capacity and of psycho-somal phenomena based on heredity.

In order to make it easier to complete twin studies on an increased number of twin sets, statistical surveys and social provisions of various kinds in favor of twins (which already have yíelded good results in Italy) are advocated.

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.

Report of the results of an examination on 34 pairs of same sex twins with special activity in sport. 21 pairs were identical (EZ), 13 non identical (ZZ). While from the 13 identical pairs (EZ) 12 were quite of the same sporting activity as even the same performance (complete concordance, K) and only one pair showed some difference in the favoured kind of sports as in the capacity (KD). From the 13 non identical pairs (ZZ) only 7 were of complete concordance (K). 4 (2 male, 2 female) of the 6 non identical pairs (ZZ) with discordances showed clearer differences in their sporting performance or in the favoured branch of sport (KD). From the last two pairs (1 male, 1 female) only one of the twins was respectively famous in sport (even one German champion!), the other thereover of a complete sporting inactivity.

The distinct differences in concordance and discordance at the examined EZ and ZZ prove, that the genotypus is of undeniable importance for sporting interest and activity as for sporting performance.

In order to confirm or to refute the produced results it seems to be necessary to examine more extended series of non selected twins.

Dupuytren's disease recurs more frequently than generally assumed. 24 typical family trees derived from the literature are analyzed here.

The main conclusions that can be derived are the following:

1) Monogenic heredity is confirmed.

2) The sex ratio in the affected families is 61,2 m: 38,8 f.

3) The sex ratio in unaffected families is 38 m: 43 f.

4) The expressivity of the disease is variable. Penetrance, which is incomplete, varies according to the sex. In our selected material, the penetrance rate is 93,6% in the males and 42,9% in the females.

5) Males transmit the gene in 68% of the cases; females in 32%.

6) Incomplete sex linkage can be excluded.

7) A comparison is made between the really observed values and the theoretical rates for normal and affected men and women for the chance of an auto-somatic dominance. These observations make possible the conclusion that the number of affected females is too low as compared with unaffected females and affected males.

8) A new theory is suggested concerning the mechanism of heredity based on the different statistical values. The responsible factor would be deadly for 60% of the XX affected zygotes. But 60% of the affected X gametes produced by the mother, being identified by an essential incompatibility for the unaffected X spermatozoid, would be electively fecundated by a Y gamate. This machanism would explain the excess of affected males, the small proportion of affected females and the sex-ratio of 61,2: 38,8.

The concordance between the observed values and the theoretically expected values of such a kind seem to convalidate our new theory.

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.

The Authors have studied 56 twin pairs (31 MZ and 25 DZ) under the aspect of the psychomotor reactions they have shown while watching motion pictures. The most closely considered reactions have been head posture, arm and leg posture and mimic reactions. The analysis of the reactions was carried out on photographs taken during the projection of the films and then compared for the degree of similarity of the postural or mymical reactions. The degree of similarity was rated according to the following scale: concordant, similar, dissimilar, discordant.

The results obtained have shown that head posture (on which the influence of conscious mobility is higher) the hereditary factors have a clear influence; while for arm posture and especially for leg posture during projection the influence of hereditary factors could not be proven in any appreciable degree; this finding is thought to be related to the low influence of conscious mobility and with the sitting position being conditioned by environmental factors.

For mimic reactions the influence of a hereditary component is always clear, but from this point of view a marked difference is found between mimic reactions to anxiogenous and to comical films. Reactions to the latter reveal a higher, characteristic degree of difference between MZ and DZ twin pairs, i. e. a higher degree of hereditary influence.

The Authors have made further studies on the family trees under the aspects of previous twinnings and of previous personal pathological anamnesis, increasing the known case histories and strenghtening the conclusions reached by Gedda in previous studies.

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.

A film has been made of 8 pairs of monozygotic and 4 pairs of dizygotic twins regarding their expression and behaviour, and we tried to examine their behaviour on genetical characters.

We do not agree, that all telencephalitic action is under control of the individuals' arbitribum; instead we stress that genetical characters are also important components.

A « plastic » adaptation to the given circumstances of the surroundings is provided by the qualitative and quantitative manyfoldednes of the telencephalon. The actions of man appear to be much more of free will than they really are.

87 affected twins (in 81 pairs) were identified among 3,982 children with pyloric stenosis. The proportion of twins among affected (1 in 46) is about the same as in the general population of births. The incidence of pyloric stenosis in partners of affected twins is 8.6 per cent, considerably higher than in the general population of births (0.3 per cent) but only slightly higher than in subsequent sibs (5.8 per cent).

The frequency of concordance is about the same in MM (4 of 31) and MF (2 of 23) pairs. Of 39 like sexed pairs 4 were concordant; the expected number of monozygotic pairs is 18 (assuming the usual proportion of monozygotic pairs), which suggests that the frequency of concordance among them is not greater than 4 in 18. It is shown that the distribution of MM, FF and MF pairs in the series corresponds closely to the distribution expected in a twin universe which contains the usual proportions of monozygotic and dizygotic twin pairs.

There are abnormal states leading to diseases that are not confined to lesions or functional defects of particular organs but that are best interpreted from a broader view as result of deficient homeostatic mechanisms. Constitutional diabetes mellitus, hypertension and obesity belong to this category. The respective homeostatic defect involves the function of many organs and is genetic in nature. In contrast tp these constitutional states diabetes, hypertension and obesity can develop also as manifestation of localized and well defined diseases of any one of the organs which are links in the chain securing the respective homeostasis. These much less common disease types are symptomatic diabetes, hypertension or obesity. There is reason to assume that the constitutional types have a multifactorial (polygenic) causation which makes further elucidation of the mode of hereditary transmission very difficult.

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.

The « Individuelle Musterwert » is stated 1951 by Brodhage-Wendt. This cipher can easily be computed from the ten fingerprints of a person.

In 100 monozygotic and 100 dizygotic twins and in 348 couples of parents with 991 children is demonstrated, that this cipher is a qualified measure to indicate the heredity of fingerprints. Furthemore the applicability of the « Individuelle Musterwert » in twindiagnosis and paternity tests is shown.

The reported data confirmed the strict linkage of Rh genes among themselves while no evidence of linkage was found between M. E. and Rh factors.

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.