The prevalences of asthma and atopy were examined in the families of 77 asthmatic and 87 control children attending a London general practice. The prevalence of asthma in first degree relatives of asthmatic children was found to be significantly higher than in relatives of control children, and this difference was more pronouced for relatives of atopic probands than for relatives of non-atopic probands. Among the relatives of asthmatics, atopic asthma was more common than non-atopic asthma, irrespective of the atopic status of the proband. However, among the relatives of control children, neither the prevalence of asthma nor the atopic status of the asthmatic relatives was influenced by the atopic status of the proband. These findings support the hypothesis that asthma and atopy are inherited independently. Although atopy itself does not predispose to asthma, it may enhance a genetic susceptibility to the condition, thus increasing the likelihood that the latter will be expressed.Two forms of asthma can be distinguished: atopic asthma in which patients give a positive immediate reaction on skin prick testing, and non-atopic asthma in which patients give no positive reactions.Although family and twin studies have established that asthma has an hereditary basisl 2 no evidence has been presented to show whether or not both the atopic and the non-atopic forms of the disease can be inherited. However, it has been shown that the prevalence of asthma is higher in relatives of atopic asthmatics than in relatives of non-atopic asthmatics.3 Therefore, if there is a genetic basis in both forms, the heritability of atopic asthma is likely to be greater than that of non-atopic asthma.Current studies suggest that this difference in heritability might arise from an increase in the susceptibility to asthma of patients who inherit a predisposition to both asthma and atopy. Pepys4 has shown that the prevalence of asthma in first degree relatives of asthmatics increases with the number of positive skin tests in the probands, indicating that atopy may enhance the manifestation of asthma. However, the prevalence of hay fever and eczema in these relatives was more strongly associated with the atopic status of the probands than was the prevalence of asthma, sug-

The role of respiratory viral infection in wheezy bronchitis was studied in 163 children, aged 0-12 years, in a London general practice. Virological investigations were also performed when these same children had acute upper respiratory illness without wheeze. A virus was isolated in 146 (26.4%/,) of 554 episodes of wheezy bronchitis, rhinoviruses accounting for almost half of the isolations. The relative frequency with which individual viruses were isolated in wheezy bronchitis was similar to that in acute upper respiratory illness in 180 other children who had never had wheezy bronchitis. The large number of isolations of rhinoviruses in wheezy bronchitis is probably due to their numerous serotypes and the absence of cross-immunity between them. Our findings have confirmed that infection by respiratory viruses can provoke wheezy bronchitis in certain children, in whom host factors are an important predeterminant. In children with a previous history of wheezy bronchitis infection by rhinoviruses was associated significantly more often with such an episode than with upper respiratory illness. The maturation of protective mechanisms, including the acquisition of specific immunity to a progressively larger number of viruses, could explain the fall in the age-incidence of wheezy bronchitis.

SUMMARYThe role of viruses and M. pneumoniae in episodes of acute respiratory illness in childhood has been studied in a London general practice. The total isolation rate was 31P7 %, but the rate varied from 32-6 % in upper respiratory infections to 640% in pneumonia. The clinical features associated with infection were influenced not only by the type of agent but also by age and other host factors in the infected children. Rhinoviruses were more commonly isolated than any other agent and were frequently associated with wheezy bronchitis.

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The McMaster Undergraduate Medical Programme is unique in several ways, and has been fully described elsewhere. There are no formal 'courses' in separate discipline areas and no statutory examinations. Emphasis is placed on the study of clinical problems (problem based learning) throughout the programme and students are encouraged to develop independent study habits. To support this programme a variety of learning resources have been developed. In this paper, one such learning resource developed by the Department of Anatomy is described. Key morphological subject areas have been identified and 'modules' assembled which contain various physical items to illustrate the subject, with instructions provided in print format or on audiotape. The materials contained in a module range from specimens, prosections, annotated charts, and models, to radiographs, pathological and histological materials, films and sIide/tape shows. Teachers are available to be consulted by the students. Self evaluation exercises are provided in the modules. This method of providing self study material is a major method of learning in morphology and is being further developed and extended into other programmes. The module has been warmly received by teachers and by students in both the Undergraduate M.D. and other Health Science Programmes.