172 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
Various articles of diet were then tried in irradiated and non- 
irradiated condition. It was proved that many, but not all, grains, 
fats, and oils, when shined upon by ultra-violet rays receive and hold 
curative properties adapted to conquer the disease of rickets. Cod- 
liver oil, then, is by no means alone as a carrier of the curative agent. 
Some modification takes place in many other kinds of foods, if 
irradiated, which makes them effective to cure rickets by indirect 
ray-therapy, fully as effectively as by the direct application of the 
rays to the skin of the patient himself. The irradiated oil may indeed 
be boiled with strong alkali and reduced to a soap and still retain 
its curative property unimpaired. 
It appears that while there are several rare chemical substances 
in cod-liver oil which possess this curative virtue when irradiated, 
the most active of them is one named cholesterol. While this sub- 
stance does not occur in plant foods, there are certain somewhat 
similar chemicals in the grains which are named phytosterols, and 
some of these have simiJar value against rickets. Not only in rickets, 
but in some allied disorders, this new discovery may prove of high 
medical value. 
As regards light therapy and rickets, the conclusions so far arrived 
at are these: 
(1) Exposure of an animal to light of wave length less than about 
3,200 Angstréms will cure rickets and also prevent its occurrence on 
a diet, that normally will produce rickets. 
(2) Cod-liver oil will act just like ultra-violet light in curing and 
preventing rickets. 
(3) Some other substances have a slight curative value in rickets, 
but most other oils—such as cottonseed oil—have no antirachitic 
value. 
(4) These oils without antirachitic value can most of them be 
made antirachitic by exposing them to ultra-violet light. 
(5) A large number of solid food materials also become anti- 
rachitic on exposure to ultra-violet light. 
(6) Cholesterol—a practically universal constituent of animal 
cells—becomes activated by ultra-violet light. So also does phytos- 
terol which is a constituent of plant cells, so that presumably food 
materials are made antirachitic by activating the cholesterol and 
phytosterol in them. 
(7) Since the human tissues contain cholesterol, the skin on ab- 
sorbing ultra-violet light has its cholesterol activated, and this acti- 
vated cholesterol, being absorbed into the blood, acts just like 
cod-liver oil absorbed from the intestines in promoting bone 
formation. 
