170 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
cure of rickets by ray therapy. As the ozone of the higher air cuts 
off solar radiation at about 2,900 Angstréms, it leaves but a narrow 
band of solar rays available. Not only in rickets but in certain 
superficial skin diseases, physicians have used with advantage the 
quartz-mercury vapor are light, which is rich in ultra-violet rays 
of these and shorter wave lengths. Recent experiments in poultry 
raising at the Maine Agricultural Experiment Station are exceed- 
ingly instructive in this line, though it would be rash to carry over 
the results unquestioned to human pathology. 
In the summer of 1924, about 250 one-week old chicks were sepa- 
rated into six groups for different treatments. Those of Group 1 
ran about in the open sunlight as they pleased, but came indoors to 
eat. The remaining five groups lived in a glass-roofed greenhouse. 
Groups 2 and 3, however, in addition to the light which reached 
them from sun and sky, were exposed for 20 minutes each day to 
the rays of a quartz mercury vapor lamp, rich in the ultra-violet. 
The remaining three groups had only the sun’s light as it came 
through their glass-roofed house. 
All the groups had the usual regular food, composed of chick 
grain, dry mash, sour milk, and rock grit, and had access to fresh 
water and sand bath. Groups, 3 and 4 were given, in addition to 
the regular diet, chopped alfalfa and grass, and Group 6 had, in 
addition to the regular diet, a small ration of cod-liver oil. 
What was the result? Groups 1, 2, 3, which had either full sun- 
hight or glass transmitted sunlight plus ultra-violet rays, all thrived. 
Groups 4 and 5 began to act less vigorously than these other's by 
the end of the fourth week. They ate with less appetite and scratched 
less. Chickens of Group 6, which had the cod-lver oil, although 
they did not relish this medicine, yet thrived better than Groups 4 
and 5, but not as well as Groups 1, 2, 3. These differences became 
more and more marked. The chickens of Groups 4 and 5 developed 
weak legs. They remained smaller in size. Their plumage looked 
rough. By the end of the ninth week, the fowls of Groups 1, 2, 3, 
all having developed normally, were about double the weight of 
the spindling chicks of Groups 4 and 5. The chicks of the first 
three groups had their bones well set and full sized, while the bones 
of Groups 4 and 5 were small, curved and weak. Chickens of Group 
6 were intermediate in their development. Fifteen deaths occurred 
in groups 4 and 5, and only one in Groups 1, 2, 3. 
Why this difference? Evidently it was solely due to some defi- 
ciency in radiation. Figure 1 shows graphically what the differ- 
ence was. A narrow band of rays in the extreme ultra-violet-—far 
beyond the extreme limit visible to the eye, and exactly in the 
region, by the way, where the ozone of the upper air begins to 
work absorption on solar rays—this little group of feeble sun rays 
