Science Record

44

The cumulative mortality curve (Fig. 3) shows the beneficial effect of screening with 3.2, 4.2, 5.3, 6.3 and 10.5 cm of lead and especially with 2.1, 74 and 95 cm of lead.

Fig. 4 shows the mean weight of the various groups of mice. To facilitate the comparison of the curves they have been shifted to the same distance corresponding to 10 g on the vertical axis. It is seen that screening with 2.1, 7.4 and 9.5 cm of lead showed no decrease in mean weight and that screening with 9.5 cm of lead produced a markedly increase in mean weight.

3, Discussion. By comparing the results of tubercle bacilli exposed to direct cosmic radiation at Jungfraujoch (3,457 m) with those at Peking (63 m), we see that the virulence was greatly decreased in the former case and not at all in the latter case. The Jungfraujoch experiment was a preliminary one; if the results were correct it means that the effect obtained was caused _-by the higher intensity of the soft component by a factor of 10 approximately as compared with sea-level, due to the altitude and latitude effects. The great decrease in virulence of the tubercle bacilli exposed to cosmic radiation under 2 cm of lead was observed as well at high altitude as at 63 m. However, at Jungfraujoch the low energy particles are absorbed by 2 cm of lead, therefore the effect obtained with 2 cm of lead was less than that obtained by direct cosmic radiation. Also the results obtained with 10 cm of lead at high altitude, where the tubercle bacilli were killed, correspond to the results obtained with - 95cm of lead at 63 m, where the virulence was decreased the most. The results obtained with 2 and 10 cm of lead correspond to the results of mice infected with tubercle bacilli! or influenza virus"! placed under 2 and 10 cm of lead. Under these conditions the lung lesions were significantly less and the mean times of survival were significantly oe when compentad with those of infected mice unscreened.

The results obtained in Fig. 2 suggest that the decrease in virulence of the tubercle bacilli was due to the number (intensity) as well as to the energy of the showers. In fact, with 1.1 cm of lead no effect was obtained, whereas with 2.1 cm of lead where the maximum intensity of electron-photon showers was present, the decrease in virulence was very great. With 3.2, 4.2, 5.3, 63 and 10.5 cm of lead the decrease in virulence was small although highly significant when compared with the control exposed to direct cosmic radiation. With 7.4 and 9.5 cm of lead where the number of showers was much less than with 1.1 and 2.1 cm of lead, the decrease in virulence was very great, which means that the penetrating showers should haye a suitable magnitude in order to produce the maximum effect.

It is not certain that there is a broad maximum between 7 and 10.5 cm of lead as one record was lost at 84 cm of lead. To ascertain this we are now repeating the experiment with 4.8, 5.8, 6.9, 7.9,.9.0, 10.0, 11.1 and 12.1 cm of lead.