SUN RAYS—ABBOT 171 
was cut off by the glass cover of the greenhouse. These indispensable 
rays were supplied in sufficient measure by the daily 20 minute 
exposures to the mercury vapor are. The want of them was partly 
made up to Group 6 by the medicine of cod-liver oil. Groups 4 
and 5, lacking both the saving medicine and the rays, languished. 
It is astonishing to remember that this very group of rays, thus 
proved so indispensable to the development of growing creatures, 
just misses being cut off from sun rays by the trace of ozone which 
exists in our upper atmosphere. So near, apparently, as this is 
the world to lacking a condition favorable to life, that if the ozone 
band, which cuts off the spectrum of the sun and stars completely 
at 2,900 Angstréms of wave length, had extended to 3,200 Ang- 
stréms in full force, the mischief would have been done. And yet 
the solar spectrum has little energy there but runs on through the 
visible and infra-red regions in great strength to 20,000 Angstréms. 
z——Light transmitted by Glass— _(Groups4, Sand 6)— — — a 
osm = SuMight (Group 1) 
<—— —Mercury Arc in Quartz _ _(Groups 2 and 3) 
Wave-lengths in Micvons 97 0.6 
Infra-red 
Spectral 
Colors 
Red Yellow Biue Vitra- 
Oronge Green Volet Violet 
Fie. 1.—Spectral colors arranged according to wave length, showing spectral limits 
of the light received by groups of chickens 
Another astonishing thing has lately been discovered. Doctors 
Steenbock and Daniels, experimenting with rats in the years 1922 
and after, were testing the value of butter fat and cod-liver oil for 
the prevention or cure of rickets. Their experiments also involved 
the use of ultra-violet light. Some of the animals having been 
radiated upon and others not, they were confined in cages in com- 
mon. The doctors were surprised to find that both sets of rats 
grew alike, except in one instance where some nonirradiated animals 
began to grow only when, after five weeks, irradiated rats were 
for the first time put into their cage. 
It seemed as if the irradiated rats were able to supply to the 
nonirradiated ones something that hitherto they had lacked. On 
trying various experiments, it was found that irradiating the air, 
or touching nonirradiated rats with their irradiated brethren did 
not give the magic curative influence. The effect was indirect, not 
a consequence of direct action on the outside of the body. Finally 
the secret appeared. Some bodily excretions of the irradiated ani- 
mals were eaten by the others and preduced the extraordinary result. 
