X. ULTRASONIC VIBRATIONS 339 



Some animals, on the other hand, are affected by ultrasonic fre- 

 quencies even though they do not produce them. Pigeons, for ex- 

 ample, are repelled by 20 kilocycle sound so effectively that this is 

 being considered as a means of driving them away from public build- 

 ings where they have proved themselves a nuisance. The same effect 

 has been observed in cats. On the other hand, it appears that simple 

 marine life like the jellyfish is attracted by intense underwater sound. 

 Man is also not immune. Various investigators (15) have reported 

 such effects as headaches, loss of balance, loss of the ability to perform 

 various mathematical computations, and a lowering of the visual light 

 threshold after exposure to ultrasonic sound (38). 



7. Miscellaneous Applications of Ultrasonics 



As far as the biological applications are concerned — the physical 

 applications are another field in themselves {2,3,19) — much has been 

 proposed and accomplished along the lines of food preparation and 

 sterilization. In some ca.ses, it has actually been possible to sterilize 

 inside the can in which the product has been sealed. Dairies use a 

 simple vibrating diaphragm that homogenizes milk and kills most of 

 the bacteria in it. The net result is a milk that forms smaller curds 

 in the stomach and is recommended for babies. Further, the bac- 

 terial count of milk has been reduced by such treatment to eight per 

 cubic centimeter while a count of 30,000 indicates a high standard for 

 pasteurized milk treated in the conventional thermal manner. Bac- 

 terial disintegration by ultrasonic sound has also been used in the 

 preparation of endotoxins and enzymes. Further use has been made 

 of the emulsifying, coagulating, and dispersive properties of sound in 

 the preparation of pharmaceutical compounds, mayonnaise, peanut 

 butter, paints, chemicals, and even in the preparation of cosmetics. 

 It has also been used in the aging of liquor. An ultrasonic process 

 has been suggested for the aging and curing of meat. 



As far as plant life is concerned, ultrasonic sound has been used to 

 accelerate and stimulate germination. Some investigators have re- 

 ported that a potato crop flowered a week earlier than control plants, 

 and with an increase in yield. Peas sprouted earlier also. 



One of the more interesting recent developments is a "seeing eye" 

 device for the blind. This instrument is essentially an adaptation of 

 underwater echo ranging equipment to airborne sound. Because 

 of the high "beaming" or directional characteristic of high frequency 



