30 TECHNICAL BULLETIN 134, U. S. DEPT. OP AGRICULTURE 
In an attempt to express in a single figure the results of combining 
the two variables, yield and toxicity, the so-called ''rat units" of 
powders have been calculated. A ''rat unit" is the yield in grams 
from 1 kilogram of fresh squill bulbs divided by the minimum lethal 
dose in grams per Idlo of body weight. It is the number of kilogi'ams 
of rats that should be Idlled by the powder obtained from a kilogram 
of fresh squill bulbs treated by the method under consideration. For 
example, if a 20 per cent yield was obtained by a certain method, and 
the powder had a minimum lethal dose of 500 milligrams per kilo 
of body weight, the rat unit for the method w^ould be calculated as 
follows : 
Yield =20 per centX 1 kilogram of fresh bulbs = 200 grams 
Toxicity = 500 milligrams per kilo = 0. 5 grams 
^ ^ Yield 200 
^* ^^^*« = T^Stj^=0:5=^^00. 
Another method for making a powder with 200 rat units would 
obviousty be less valuable, being but half as efficient. The rat units 
determined for a number of series of samples are given in Table 14. 
Table 14. — Yields of toxic squill powders 
Sample 
No. 
Method of 
drying 
Yield 
Mini- 
mum 
lethal 
dose 
Rat 
units 
Mg. 
per 
kgm. 
Per 
of body 
P. C. 
cent 
weight 
761 
Fresh bulb 
4,000 
250 
7iyA 
Electric oven... 
23.2 
1,000 
230 
719AF... 
do... 
17.8 
2,000 
90 
719AAF.. 
do.. 
12.0 
2,000 
60 
766 
Desiccator 
23.5 
1,250 
190 
719A 
Electric oven... 
23.2 
1,000 
230 
720A 
do. 
12.0 
250 
480 
721 A 
do 
12.9 
350 
370 
722 A 
do 
21.5 
500+ 
430— 
723 A 
do.... 
24.4 
1,000+ 
240— 
719B 
do 
21.5 
625 
350 
720B 
do.... 
10.1 
250 
400 
721 B 
do 
11.9 
400 
300 
722B 
do.". 
20.7 
350 
590 
Sample 
No. 
Method of 
drying 
Yield 
Mini- 
mum 
lethal 
dose 
Rat 
units 
Mg. 
per 
kgm. 
Per 
of body 
P. C. 
cent 
weight 
723B 
Electric oven... 
22.3 
500 
450 
727A 
do... 
23.9 
500 
480 
762 
do 
19.5 
750 
260 
774 
do 
22.5 
1,250 
180 
763 
do.... 
22.5 
750 
300 
764 
do 
22.0 
2,000 
110 
782 
do 
21.0 
1,250 
170 
765. 
do 
23.5 
1,250 
190 
724A 
Steam oven 
21.5 
500 
430 
725 A 
do 
20.6 
500 
410 
760 
do 
20.4 
500 
410 
770 
do 
22.2 
750 
300 
775 
do 
21.2 
625 
340 
The rat unit for the fresh bulb (P. C. 761) was 250. Essentially 
the same value w^as obtained for P. C. 719A in the unfermented stage. 
Fermentation to the alcoholic stage reduced the rat unit to 90, and 
further fermentation to the acetic-acid stage caused a drop to 60, 
showing the loss in activity during fermentation to be progressive. 
Freezing caused a decrease to about 200 rat units. The rat units of 
powders prepared under laboratory conditions ranged from 110 to 
590, while the values for powders made under semicommercial condi- 
tions ranged from 300 to 430. Attention to manufacturing details 
would be expected to raise the rat units for commercial powders 
above 500. Indeterminate values for two of the P. C. No. 719 
series prevent careful comparison, but the A series averaged less than 
350, whereas the B series averaged 420 rat units. This would sug- 
gest that preliminary air-drying treatment given the B series pre- 
served the toxicity or aided in its development. The fact that 
