184 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1946 
radiations are of many types (alpha, beta, gamma, neutron, and 
positron). Many biologically useful radio elements are produced by 
deuteron bombardment and include radiophosphorus, radiosodium, 
radioiron, radioiodine, and radiostrontium. These substances can be 
administered to patients and their exact method of localization and 
storage in the human body studied by means of Geiger counters and 
similar apparatus. In this manner the metabolism of certain living 
tissues, in both health and disease, can be studied more completely 
than ever before. For example, totally new information concerning 
the need for and method of use of iron in the human pee in conditions 
like anemia, has been obtained. 
An indirect development of high-voltage tubes in physics is the 
electron microscope which permits much higher magnifications of 
minute objects than are feasible with optical microscopes. With this 
instrument the image of the object is viewed either on a fluorescent 
screen or is recorded on a photographic film. Recent developments 
include modifications by which the instrument may be used either as 
a diffraction camera or a microscope. Stereoscopic electron micro- 
graphs can be made. The usual electron microscope operates at about 
60 kilovolts, but there is a small table model operating at 30 kilovolts. 
The structure and behavior of viruses has been studied for the first 
time, and the detailed structure of bacteria has been revealed. 
Chromosomes, the tiny rodlike particles that bear the major responsi- 
bility for inherited characteristics, may be examined, and by means of 
ingenious methods the actual location of certain specific genes in a 
number of chromosomes has been determined. 
Biology.— X-rays have been used in most of the various biological 
sciences, notably in botany and zoology. The architecture of many 
torms of plant life have been studied by macroradiography as well as 
microradiography. Mutations have been produced by bombardment 
of seedlings and rootlings with X-ray, and new hybrids successfully 
developed. In fact, one physician insists that a special type of be- 
gonia he grows is a direct result of irradiation of a former plant. He 
gives no credit to Mendel’s cosmic ray but, unfortunately, I am not 
sufficiently familiar with botany to know whether or not he is correct. 
In zoology, several forms of animal life have been studied with 
X-rays. With the larger type of animal one naturally has to make 
segmental studies. About a generation ago an ailing elephant at the 
London zoo was subjected to X-ray examination. The tired pachy- 
derm lay on her side and had her torso marked with chalk into a 
series of rectangles, each a little less than 14 by 17 inches in size. These 
then were numbered in sequence and a series of roentgenograms made. 
We cannot vouch for the quality of the films made through the thicker 
parts, but those of the extremities which we saw were quite good. Race 
