216 



The Absorption of Electromagnetic and Ultrasonic Energy /I I : 5 



this discrepancy by stating that there are a large number of different 

 relaxations which occur with a fairly uniform distribution of relaxation 

 frequencies. At best, this explanation is highly artificial because the 

 origin of these relaxations is unknown. It is possible that a more com- 

 plete model of protein structure might increase the understanding of this 

 process. Conversely, these apparent relaxations are one type of data 

 that can be used to test any theory of protein structure. (The structure 



E 

 o 

 5 1.00 



-v. 



J. 7 



<D 

 CL 



C 



o 

 o 



c 



o 



c 



<3 



0.10 



•§ 



■ Liver Nuclei 

 -Liver Tissue 



Blood,,— 



Liver Homogenate 



Plasma 

 Cone, Hb 

 Dilute Hb 



Gelatin 



_L 



2 3 5 7 |0 



Frequency (mc) 



Figure 6. Ultrasonic absorption of various suspensions and of 

 liver tissue. (To convert nepers to db, multiply by 8.7.) 

 After E. L. Carstensen, with permission. 



of proteins is discussed on the basis of X ray and chemical data in 

 Chapter 17.) 



Measurements on the values of pc and the absorption coefficients for 

 a wide variety of soft tissues are summarized in the reference by Goldman 

 and Heuter. These authors show that many measurements in various 

 laboratories all support the similarity of pc for tissue and water. Simi- 

 larly, all of these measurements indicate the relatively small dependence 

 of the absorption per wavelength on frequency in the range 0.25 to 25 mc. 

 The values for this absorption for many tissues are higher than that for 

 blood. Whether this is due to differences in the proteins or to scattering 

 at the cell walls is not known. Typical values for ultrasonic absorptions 

 are shown in Figure 6. 



A comparatively small number of isolated measurements at frequencies 

 below 1 00 kc indicate that the absorption per wavelength is proportional 

 to the frequency in this range. If this is proved to be the case, it would 



