72 Applied Biophysics 



example, an electric lamp (giving a radiation maximum at 

 ^ l.Sji) with an electric fire (giving a radiation maximum 

 at '^ 3\i). Mayneord and Tulley ^ have approached this prob- 

 lem by studying the al)sorption of radiation of different tempera- 

 tures in various thicknesses of celluloid. However, as they point 

 out, care must be taken in the interpretation of the results be- 

 cause of the scatter of radiation in this medium. This difficulty 

 is, of course, aggravated in the case of infrared radiation which 

 is not administered in a beam. Secondary radiation from the 

 filter may also cause falsification of results. 



We have made preliminary ex])eriments on the transmission 

 by various types of textile materials (blankets, towels, cotton 

 and linen sheets, lint, etc. ) and find that, in general, materials 

 transmit 20-30% of the long-wave incident radiation, and 30- 

 40% of the short-wave. However, if a patient is covered by a 

 blanket, it must not be assumed that he will only receive, say 

 25%, of the energy incident on the upper surface of the blanket. 

 In addition, the blanket will gradually warm up to a temperature 

 depending on the particular circumstances, and will transmit 

 energy, not only by secondary radiation, but also by conduction, 

 both by direct contact and across air pockets trapped between 

 the blanket and the skin. 



What is of importance is the total heat supplied to the patient 

 by all mechanisms, and we have been able to evaluate the dif- 

 ferent contributions in one case. Before an open electric fire we 

 found that a layer of lint transmitted 27.5% of the incident 

 radiation, and that conduction was responsible for transmitting 

 an amount of heat equal to 32% of the incident radiation. In 

 this case the covering was not enclosed, and so the lint did not 

 acquire a high temperature, and did not in consequence provide 

 any appreciable amount of reradiation. The total energy received 

 on a calorimeter placed behind the lint was. in this case, 60% 

 of the incident radiation. 



