Radio-activity and Normal Physiological Function. 
< BY 
V, H. BLACKMAN. 
T HE radio-active substances, or radio-elements as Soddy calls them, are 
characterized by the spontaneous and continued discharge of rays or 
particles which are projected from them with various speeds, sometimes with 
a velocity as great as that of light. The view put forward by Rutherford 
and Soddy in 1903, that this peculiar activity is due to a process of atomic 
disintegration, is now universally accepted. The rays projected are of three 
types — a-rays, / 3 -rays, and y-rays, some elements like radium and uranium 
giving off all three, while others exhibit only a single kind. 
The a-rays or particles are projected with great velocity, but are easily 
absorbed by thin sheets of metal. The a-particle is now known to be 
a helium atom (at. wt. = 4) carrying two unit charges of positive electricity ; 
hence the term positive rays is applied to them. The / 3 -rays are more 
penetrating than the a ones ; they are known as negative rays, for they con- 
sist of negatively charged particles, in fact they are electrons. The y-rays 
are similar to X-rays, being light waves of very short wave-length, only one- 
thousandth of that of visible light. 
One would expect that the rays projected from the radio-elements 
would have a marked physiological action, and we find that they will 
coagulate protein, will cause 4 burning ’ of the skin, and other deleterious 
physiological actions. It is also well known that radio-active substances 
have been used in the control of cancer, and that plants are markedly 
affected by exposure to these substances. 
Most of the radio-active elements, like radium, actinium, and thorium, 
have high molecular weights and are not normally found in either animals 
or plants, so that their radio-active processes cannot be considered part of 
the normal physiology of the organism. In 1907, however, it was shown by 
Campbell and Wood that radio-activity is not confined to the heavy 
elements, but that potassium and rubidium emit ( 3 - rays ; those of potassium 
having a penetrating power about equal to those of uranium, but of an 
intensity only about one-thousandth of that of an equal weight of that 
element. Now potassium is an element which is a constituent of the bodies 
[Annals of Botany, Vol. XXXIV. No. CXXXV. July, igao.J 
X 
