['-12-', 'The', 'twin', 'approach', 'is', 'no', 'guarantee', 'for', 'a', 'complete', 'group', 'comparability.', 'It', 'is', 'so', 'in', 'the', 'groups', 'of', 'identical', 'twins', 'as', 'far', 'as.', 'genetic', 'factors', 'are', 'concerned,', 'and', 'it', 'is', 'further', 'reasonable', 'to', 'assume', 'that', 'the', 'smoking', 'discordant', 'identical', 'twins,', 'in', 'spite', 'of', 'their', 'discordant', 'smoking', 'behavior,', 'experience', 'a', 'far', 'more', 'similar', 'environment', 'than', 'do', 'smokers', 'and', 'non-smokers', 'in', 'general.', 'This', 'assumption', 'was', 'supported', 'by', 'some', 'findings', 'in', 'the', 'actual', 'twin-study,', 'but', 'the', 'number', 'of', 'factors', 'studied', 'was', 'too', 'small', 'to', 'give', 'a', 'conclusive', 'evidence.', 'We', 'still', 'have', 'to', 'deal', 'with', '"self-selection",', 'and', 'the', 'member', 'of', 'the', 'pair', 'who', 'chose', 'to', 'become', 'a', 'smoker', 'may', 'as', 'well', 'have', 'chosen', 'to', 'expose', 'himself', 'to', 'other', 'habitual', 'factors', 'relevant', 'to', 'disease.', 'Ongoiing', 'research', 'will', 'throw', 'further', 'light', 'on', 'this', 'question.', 'The', 'data', 'from', 'the', 'actual', 'twin', 'investigation', 'showed', 'a', 'decreased', 'difference', 'between', 'smokers', 'and', 'non-smokers', 'in', 'regard', 'to', 'the', 'two', 'symptoms', 'studied.', 'The', 'hypermorbidity', 'in', '"angina', 'pectoris”', 'that.', 'was', 'found', 'amoung', '"smokers', 'in', 'general"', 'could', 'not', 'be', 'detected', 'in', 'the', 'series', 'of', 'smoking', 'discordant', 'twins.', 'It', 'should', 'be', 'mentioned', 'here,', 'that', 'a', 'control', 'analysis', 'showed', 'that', 'the', 'smoking', 'twins', 'in', 'the', 'smoking', 'discordant', 'twin', 'series', 'smoked', 'on', 'an', 'average', 'just', 'as', 'much', 'as', 'did', 'the', '"smokers', 'in', 'general",', 'which', 'implies', 'that', 'the', 'decrease', 'in', 'hypermorbidity', 'cannot', 'be', 'ascribed', 'to', 'differences', 'in', 'exposure', 'load.', 'I', 'am', 'personalily', 'convinced', 'that', 'this', 'decrease', 'of', 'the', 'hypermerbidity', 'is', 'a', 'reflection', 'of', 'an', 'improved', 'group', 'comparability,', 'but', 'I', 'would', 'not', 'argue', 'at', 'this.', 'point', 'whether', 'this', 'jis', 'due', 'to', 'the', 'control', 'of', 'the', 'genetic', 'constitution', 'or', 'to', 'a', 'parallel', 'control', 'of', 'the', 'environment.', 'As', 'for', 'the', 'symptom', '"cough"', 'the', 'hypermorbidity', 'decreased', 'measurably,', 'but', 'not', 'as', 'far', 'as', 'to', 'unity.', 'Ini', 'view', 'of', 'what', 'was.', 'discussed', 'above', 'about', '"susceptible"', 'and', '"non-susceptible"', 'individuals,', 'a', 'certain', 'decrease', 'was', 'of', 'course', 'expected', 'in', 'a', 'series', 'of', 'identical', 'twins.', 'The', 'still', 'existing', 'hypermorbidity', 'reveals,', 'bes2.eFSooT', ' ']