No. 7.— CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY 
OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD 
COLLEGE, UNDER THE DIRECTION OF E. L. MARK, No. 228. 
Effects of radium on living substance.—I1. The influence of radia- 
tions of radium upon the embryonic growth of the pomace-fly 
Drosophila ampelophila, and upon the regeneration of 
the hydroid Tubularia crocea. 
By E. D. Conepon. 
Introduction. 
These studies on the effects of radium, the first two of which are 
here published, were begun in 1906, at the suggestion of Professor 
Mark. The work was carried on under his direction in the Zoélogical 
Laboratory at the Museum and in conference with Prof. Theodore 
Lyman of the Jefferson Physical Laboratory. The results on other 
parts of the work are reserved for further experimentation before 
publication. 
Space does not permit here an extended description of the three 
types of radiation given off by radium, the alpha, beta, and gamma 
rays. According to the commonly accepted corpuscular theory of 
matter, two of the three, the alpha and the beta, consist of particles 
of matter. The third, the gamma rays, are movements of the ether. 
The alpha rays are so little penetrating that a few sheets of paper 
will absorb them; the beta rays, on the contrary, are more penetrat- 
ing and may even traverse a considerable thickness of metal. The 
gamma, radiations exceed the beta rays, as well as X-rays, in their 
penetrating power. The larger portion of the energy emitted by 
unscreened radium is in the form of alpha rays. Further information 
as to radium and its radiations may be found in such standard works 
as Rutherford’s Radioactivity and his Radioactive Transformations. 
In spite of the numerous investigations on the biological action 
of the three types of radium rays which have appeared since the early 
notices from Becquerel and others, not much progress has been made 
in analyzing their action. This is evident from the fact that we 
know almost nothing of their distinguishing biological effects other- 
