X. ULTRASONIC VIBRATIONS 335 



absence of bubble formation in the gelatin solution, which would re- 

 sult in smaller absorption even with greater viscosity. One other 

 interesting point is the change with frequency in a/P for fat tissue 

 plus muscle (Table V). This does not occur for most pure substances. 



Other investigators have found that the marrow of the bone may 

 be heated without affecting the bone and have proposed this as being 

 useful in medical diathermy. Pohlmann {SO) has designed a hand 

 applicator (see Fig. 8) in which the vibrating crystal is held directly 

 against the skin for sciatic and plexus neiu-algia. He further recom- 

 mends the use of a contact substance such as paraffin oil or linament 

 between the massager and the skin. Excellent results have been re- 

 ported for such treatment. 



Regarding production of heat by absorption, Lynn, Zwemer, and 

 Chick {21) reported interesting results with a focused quartz crystal 

 at a frequency of 835 kilocj^cles. The crystal w^as ground to provide 

 a definite focal point for the sound waves emitted by the surface (see 

 Sect. B2 and Fig IE) and the sound passed out through a Cellophane 

 diaphragm so that direct contact could be made with the tissue. In- 

 tense heating at the focal point was shown by exposing blocks of 

 paraffin and liver to the sound beam. The paraffin melted and the 

 liver "cooked" white at the focal point. Examination with a micro- 

 scope showed destruction of the cells at the focal point and in the path 

 of the beam. 



In experiments with living animals, production of lesions is made 

 difficult by circulating blood. For this reason, the brain of a dog w^as 

 chosen since any destructive effects would become evident by a dis- 

 turbed motor activity as soon as the effects of the anesthetic dis- 

 appeared. Despite the fact that the focus was disturbed by bone re- 

 fraction and scattering, positive results were obtained. With trans- 

 cranial application of the focused sound beam to the proper areas of 

 the cerebral cortex, disturbances in muscular coordination, some 

 paralysis, and, in one case, blindness were observed. These were 

 associated with the corresponding brain lesions. Necrosis of the 

 scalp also occurred where the apparatus was applied. 



3. Chemical Effects of Ultrasonics and Secondary Results of 



Cavitation 



The acceleration of chemical reactions by ultrasonics has been 

 shown to be due to cavitation in the pi-esence of dissolved gases. 

 The majority of these reactions are oxidations such as the conversion 



