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National Resources Planning Board 



composed of an intimate mixture of substances, where 

 it is desirable to estimate at a glance the relative com- 

 position. It is much used in the textile industry in 

 this way. The absorption ultraviolet microscope finds 

 its greatest use in medicine. 



The very great industrial and medical importance of 

 X-rays is well knowTi. In this field perhaps more than 

 any other, further investigations of the biophysicist are 

 needed, on both the medical and the industrial sides. 

 The subject of rontgenographj'^, the taking and the 

 interpretation of clinical X-raj' photographs, has be- 

 come a science within itself, of the very highest im- 

 portance for industrial medicine. No tool is so useful 

 as the X-ray tube in the diagnosis of industrial injuries, 

 and none, perhaps, has been so rapidly or so markedly 

 developed within recent years. In this work the 

 biophysicist has had, and wUl continue to have, a con- 

 trolling part, for no field demands a more intimate com- 

 bination of physical, biological, and medical knowledge, 

 and in no other field are the requirements in regard to 

 the accuracy and the completeness of information in 

 these various fields on the part of the worker more 

 strict. Very recent developments, such as the modern 

 extremely high voltage X-ray tube, various techniques 

 of stereoscopic photography, and constantlj' changing 

 techniques of interpretation of rontgenograms, are aU 

 indicative of the rapid development of the field and 

 the activity of biophysical research in it. 



The second great biological application of X-ray 

 techniques, and perhaps the most wndely known, is to 

 cancer therapy. Here too the biophysicist is of pi-ime 

 importance in a subject very close indeed to uadustry. 

 The requirements for the treatment of deep-seated 

 tumors have given great stimulus to the development 

 of the technique of producing high-voltage X-rays, and 

 have influenced X-ray tube design as much as any other 

 factor. Recentlj', the application of new types of high- 

 voltage sources, such as the Van de Graaf generator, 

 has brought about interesting advances. Much work 

 has been done in the impregnation of tumors with the 

 salts of elements of high absorbing power for X-rays, 

 with the purpose of trapping as much energy as possible 

 within the tumor mass. 



Quite as important as the influence of biophysics on 

 X-ray tube design has been its development of tools for 

 measuring total applied X-ray dosage, upon which 

 X-ray therapy has depended for its quantitative inter- 

 pretation. Extensive researches in various forms of 

 ionization chambers have evolved types which are com- 

 pact, portable, easily used, and quite accurate as rela- 

 tive standards, and other, more bulky designs which 

 yield accurate absolute measurements and serve as 

 calibration standards. These designs have been taken 

 over into industrial uses quite apart from the medical 

 services which they were originally expected to perform. 



A third application of biophysics in the field of X-rays, 

 which gives interesting promise and is as yet in the 

 very preliminary stages of its development, is the pro- 

 duction of mutations in various crop plants of interest 

 by irradiation of germ cells. It has been demonstrated 

 that new forms of plant life can be produced in this 

 fashion which will have the true characteristics of in- 

 duced mutations. They will breed true to the new type 

 for an indefinite number of generations after the irradi- 

 ation has been performed, and m some cases the muta- 

 tion may be such as to enhance the commercial value 

 of the altered product. A thorough estimate of the 

 commercial practicabilitj- of this procedure must be 

 left to the biophysicist of the future. 



Cathode rays have been used by the biophysicist in 

 applications on the whole very similar to those of X-rays 

 and ultraviolet. It has been found that cathode rays, 

 like ultraviolet light, will increase the vitamin content 

 of irradiated sterols, although the very limited pene- 

 trating power of the beam sets a definite limit to the in- 

 dustrial practicability of the method. Cathode rays, 

 again like ultraviolet light, cause fluorescence in many 

 materials, and this property finds industrial applicabil- 

 ity. Mutations can also be produced under cathode 

 irradiation. Finalh", cathode rays have been shown to 

 have definite therapeutic value in certain cases of skin 

 cancer, where, because of the very high absorption of 

 their energy over short distances, they may be of greater 

 value than X-rays. 



Newest of all the radiations to be considered as a 

 practicably useful tool by the biophysicist is the neu- 

 tron, and here the possibilities are almost unexplored 

 and are highly exciting. Very little information has as 

 yet been obtained of the therapeutic value of neutrons, 

 but experiments of many types are very actively under 

 way. A property of neutrons of great interest is their 

 power of inducing artificial radioactivity in elements of 

 importance to the physiologist. This quality has made 

 possible the initiation of a wide program of biophysical 

 experiments with the so-called tracer elements, in which 

 the progress of the element through the human, animal, 

 or plant body can be accurately traced and recorded 

 with ionization counters, by virtue of the energy 

 spontaneously released by the radioactive element. 

 Researches of this sort are, of course, by no means 

 confined to biological subjects, and may find important 

 industrial applications, such as in the detection of minute 

 traces of various impurities in metals, and the study of 

 the rate of passage of substances through othi-r sub- 

 stances. These developments have in turn initiated 

 further intensive research in the perfection of the design 

 of Geiger counters, to mcrease their sensitivity^ and 

 their range, which in its turn may have important indus- 

 trial repercussions. Finally, the use of neutrons in spe- 

 cial types of rontgenography seems a definite possibil- 



