§25-] 
TOXIC ACTION AND CHEMICAL COMPOSITION. 
35 
The partition coefficient can be estimated chemically or physiologically 
by the following simple methods :— 
(a) Non-volatile solid substances soluble in water.—Dissolve 1 grm. in 
50 c.c. of water ; add an equal bulk of olive oil ; shake ; then allow the 
oil to separate, and take of the aqueous solution a known volume, say 
10 c.c., and evaporate to dryness ; weigh the residue. 
If the original strength of the aqueous solution be designated as a, 
and after shaking with oil the concentration be represented as b, then 
a—b 
the partition coefficient is equal to -. 
b 
Example .—A solution had a strength of 2 per cent, before shaking 
and of 0-2 per cent, after shaking ; 
partition coefficient equals 
(b) Solid substances more soluble in oil than in water. —In this case 
only 1 volume of oil is taken to 10, 50, or 100 of water, the ultimate 
result being multiplied accordingly. 
(c) Fluid substances soluble in oil and in water , and not too volatile .— 
10 c.c. of the fluid are shaken with 50 c.c. of oil and water in a graduated 
burette and the increase in volume of the oil noted. The volume of 
the water is noted ; the increase of volume of the oil divided by that 
oil 
of the water gives the coefficient -. 
water 
(d) Physiological method. —Tadpoles as compared with leeches or 
species of worms belonging to the genus Nais are used. As a rule, a 
leech requires double the dose necessary to narcotise a tadpole. An 
aqueous solution of the substance is made of such strength that it will 
just narcotise tadpoles = ft ; another which will narcotise leeches, say 
2/3. If the original concentration of the liquid equals a, and after 
shaking with oil -= 6 ; if this b solution narcotises tadpoles but does 
not narcotise leeches, the concentration evidently lies between ft and 2ft ; 
the solution is now diluted with a measured quantity of distilled water 
until the tadpoles show signs of recovery. From the amount of added 
water the concentration b is calculated, and the partition coefficient 
obtained. That the narcotic action to a great extent is parallel with 
the solubility in oil is well shown by a research of H. Meyer on tadpoles, 
in which the coefficient of each of the substances experimented with 
was also ascertained. 
§ 25. In some cases the increase of CO groups weakens the action 
of a poison ; thus, in allantoin there are three carbonyl (CO) groups ; 
this substance does not produce excitation of the spinal cord, but it 
heightens muscular irritability and causes, like xanthine, muscular 
rigidity ; alloxantine, with a similar structure but containing six car¬ 
bonyl groups, does not possess this action. 
