536 LEO E. LIPETZ 



changes the properties of its surface membrane and causes the generation 

 of nerve impulses. 



Such mechanisms require that stored energy be available; in this case, in 

 the form of ion concentration gradients. The metabolic processes that built 

 up such concentration gradients are made possible only by the organization 

 of the cell. At the same time, this organization also limits the number of 

 mechanisms by which stored energy can be discharged. 



At tissue and organ levels, the importance of organization is obvious. The 

 visual system no longer responds to light if the retina is replaced by a piece 

 of dermis, for example. 



At the organismic level, subtle changes in organization can produce large 

 changes in response. A human subject might be repeatedly exposed to a flash 

 of light and never once push the button. But, if the experimenter now merely 

 says to him, "When you see a light, push the button," the subject will then 

 push the button after every flash. The structural change that occurred in 

 the organization of the organism is presently beyond our powers to specify, 

 yet the change in the effect of a given radiation stimulus on the system was 

 overwhelming. 



As these examples show, the visual system is so organized at all levels as 

 to be extremely sensitive to light, that is, to give readily detected responses 

 on exposure to low doses of light. It does this by using the energy of the 

 light to trigger the release of a larger amount of energy, and this to trigger 

 the release of still larger amounts, so that even within the visual system 

 proper an energy amplification of 10^ may be obtained. 



This sensitivity need not be limited to light. Anything that could trigger 

 the initial energy release in the sequence would give the same effect. Ionizing 

 radiation can do this, apparently by breaking up the visual pigment molecule 

 (Lipetz, 1955a), with the result that normal visual resjx)nses can be ob- 

 tained with as little as 0.5 mr of x-rays. Table I lists the quantitative studies 

 that have been made of normal visual responses evoked by high energy 

 radiations. 



The great sensitivity of the vislual system depends on the high specificity 

 of its organization. Since that specificity can be disturbed by comparatively 

 low energy agents, very little energy should be required to produce reduc- 

 tions in the sensitivity of the visual system. Indeed, objectively observed 

 decreases have been produced with as little as 10.5 r. Table II lists the 

 quantitative studies of damaging effects of high energy radiations on visual 

 function. 



A final word of warning: the second clearest principle that has emerged 

 from the study of vision is that the organization, at all levels, is in a state of 

 flux. For some time workers in visual research have been familiar with the con- 

 stant exchange of atoms in a molecule, the slow growth and development 



