THE PERCUTANEOUS ABSORPTION OF SALICYLATES 101 shown in Fig. 2 and the equation employed. Please notice that the inter- cepts at T = infinity give the theoretical maximum plasma levels for each concentration while the intercepts at the abcissa give the minimum times required for salicylic acid to become detectable in the blood. T,v. Evr•.cT or AR•.A When the same quantity of material was employed, but the area was re- duced by 50 per cent, a distinct decrease in absorption was obtained. This is shown in Fig. 5. 50.0 l I I FULL ARE 40.0 - L ,!! 20.0 j !/ J o.o I """" 0 '•" I I I TIME (HOUFIS) 5.•Effect of area on the percutaneous absorption o• 10• methyl salicylate in m•neral oil. Fig. 50 4O 30 2O t IO i I •IGM. - 2 GM. 0.5 GM. ,/, - 0 I I I TIME (HOURS) Fig. &--Effect of varying the amount of the mixture of 10% methyl salicylate in mineral oil on the percutaneous absorption of methyl salicylate.

102 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS THE EFFECT OF QUANTITY OF THE PP. EP.4P. ATION USED When 0.$, 1 or 2 grams of 10 per cent methyl salicylate in mineral oil were applied to the same area, there were no significant differences in the rate of absorption (Fig. 6). THE EFFECT OF THE VEHICLE Highly volatile vehicles evaporate leaving a high bulk concentration of drug on the skin. This was clearly the case when methyl salicylate was i i i i 140 - • - ,oo.• - • •oo- • • - so- - • _ • •0 - I 5 I0 15 30 60 I 5 I0 15 30 $0 TI ME (MINUTES) Fig. 7.--Percutaneous absorption of methyl salicylate from 100% methyl salicylate and 10% methyl salicylate in ether. • 50 • .o g_• 3o cn 20 i i i - NO PRE-TREA--PRE-TREATMENT•'•' - _ • WITH ETHER I I I 2 TIME (HOURS) Fig. 8.--Effect of pre-treatment with ether on percutaneous ab- sorption of 10% methyl salicylate in mineral oil.