MEDICAL APPLICATION 127 



large proportion of ultra-violet rays, have been employed as 

 germicides in surface wounds. The penetrating power of these 

 rays is slight, and, therefore, they can have little effect on deep- 

 lying structures. Nevertheless their action on certain bacilli have 

 been somewhat extensively studied. Typhoid bacilli are killed 

 by exposure to rays of wave-length 2100 2800 Angstrom units. 

 Bacilli vary in vulnerability, e.g. on exposure to light from a 

 Cooper-Hewit (mercury vapour) lamp placed 12 cm. above them, 

 b mucosus capsulatus was killed in 20 sees., staphylococcus aureus 

 in 90 sees., while 150 sees, elapsed before the death of b subtilis. 

 Lupus (tubercular ulceration), carcinoma and other morbid 

 growths are occasionally treated with ultra-violet light. It is 

 worth while noting that normal cells equally may suffer through 

 exposure to rays over 2800 Au. Digestive enzymes are killed. 

 Protection may be provided by passing the light through 1 per 

 cent, solutions of gelatine-peptone, amino-benzoic acid, cystine, 

 tyrosine and leucine. Tyrosine has especially good detoxifying 

 action in alkaline solution. These solutions absorb rays of wave- 

 length 2480 2710 A. and so reduce the toxicity and bactericidal 

 action of ultra-violet light. 



Similarly, X-rays have a strong lethal action. Pioneers in 

 radiography suffered from this action. There is no doubt as to 

 the power of the X-rays to kill ft-typhosus suspended in water, 

 or to inhibit the growth of tumours. But care has to be exercised 

 in their application. For instance, a number of mice were arti- 

 ficially immunised against a transplantable carcinoma. Half of 

 them were then exposed to the X-rays. It was found that the 

 mice so exposed had lost their immunity and had been rendered 

 susceptible to carcinoma while the controls were still immune. 

 Animals which have been X-rayed repeatedly are generally more 

 susceptible to certain diseases than unexposed animals, e.g. 

 monkeys more readily develop poliomyelitis after being exposed 

 to the X-rays. 



The rays emitted by radio-active elements, especially radium, 

 have been employed more extensively in the treatment of morbid 

 cell growths than either ultra-violet light or X-rays. The cells 

 are not killed outright but division of the nuclei is inhibited, 

 eventually leading to death of the cell. The successful treatment 

 of cancer patients by radium is well known. The rays of radium 

 are capable of causing definite regressive changes in deep seated 

 tumours such as mediastinal lympho-sarcoma, carcinoma of the 

 lungs, and abdominal metastases of carcinoma of the testis. 



