SEPTEMBER 20, 1918] 
coincident for a relatively short period of time 
only, a few white “spottings” at a distal end 
of the leaflets may result; if the time element 
is lengthened, all the cells of the leaflet may 
suffer a water loss much below the wilting co- 
efficient, and instead of a “spotted” appear- 
ance the entire leaflet will bleach white. This 
is exactly what happens under both experi- 
mental and field conditions. In the intermoun- 
tain country where a very large number of ob- 
servations have been made, it has been noted 
that fields showing a considerable incrustation 
of alkali when irrigated exhibited white spot in 
more or less amount, depending upon the other 
environmental factors above mentioned. Also, 
a sudden rise of the water table in irrigated 
districts has brought about the same appear- 
ance of the plants in the fields. Some very in- 
teresting observations have been made on fields 
adjacent to each other, with plants of the same 
age and all conditions the same excepting the 
application of water. The irrigated fields 
showed extensive white-spot trouble, while the 
non-irrigated fields showed none. 
It has been noted by eastern pathologists 
who have made observations on this disease 
that it occurs mainly in the spring of the year. 
However, the writer has observed it in the 
intermountain districts during the early 
spring, during mid-summer and during the 
late fall; in short, throughout the entire grow- 
ing season. 
Specimens of artificially produced white spot 
of alfalfa were submitted to several plant 
pathologists who reported that these specimens 
were identical with diseased alfalfa plants 
which they had themselves collected. 
An extended report will be published in due 
time after the completion of certain experi- 
ments which are now in progress. 
P. J. O’Gara 
AMERICAN SMELTING AND REFINING Co., 
Savt Lake City 
THE POLYHEDRAL VIRUS OF INSECTS WITH A 
THEORETICAL CONSIDERATION OF FIL- 
TERABLE VIRUSES GENERALLY 
In a previous paper’ J. W. Chapman and I 
called attention to the fact that the wilt or 
1 Biol, Bull., Vol. XXX., No, 5, pp. 367-390. 
SCIENCE 
301 
polyhedral disease affects many different spe- 
cies of insects. We also showed that the dis- 
ease is not produced by bacteria, but is caused 
by minute organisms capable of passing 
through diatomaceous filters, and further at- 
tempted to demonstrate that the polyhedral 
bodies always found associated with the dis- 
ease are not organisms, as supposed by Bolle, 
Fischer, Marzocchi and Knoche, but reaction 
bodies—simply nucleoprotein by-products. 
In order to satisfy myself that we were 
really dealing with an organism and not merely 
with an enzyme, toxin or other material a 
large series of passage infections were insti- 
tuted. Twenty-five gipsy moth caterpillars 
were infected at a dilution of 1: 1,000 with ma- 
terial obtained from a caterpillar previously 
dead of wilt. The animal was merely ground 
up, sterile water added and the whole filtered 
through a sterile Berkefeld grade “N” candle. 
All twenty-five caterpillars fed with the filtrate 
died typically of wilt during the course of 
three weeks, whereas twenty-five controls fed 
with the autoclaved filtrate lived, pupated and 
transformed into moths. One animal dead in 
this first series was prepared, the material di- 
luted as before (1: 1,000), filtered and fed to 
another series of twenty-five caterpillars. The 
experimental animals all succumbed, whereas 
the controls did not. Third and fourth pas- 
sage infections were performed and the results 
were similar with the exception that the period 
from infection to death was considerably 
shorter at the fourth passage than at the first 
three. This shortening of the time between 
infection and death seems to point towards an 
increase in virulence with successive passages. 
There are certain autocatalytic substances 
like chromatin that increase progressively, so 
to the physiologists my passage infections may 
not necessarily be proof for the contention 
that I am dealing with parasitic ultra-micro- 
scopic organisms. However, if one reviews the 
field of the filterable viruses? and compares all 
of the results obtained by other workers with 
my results, one can not but feel inclined to 
2 Thirty-two diseases are now known to be caused 
by filterable viruses. 
