NON-PROTOPLASMIC CELL CONTENTS 101 
vessels, of many plants. It may contain starch, sugar, proteid, 
oil, enzymes, bitter principles, tannins, alkaloids, gum, resins, 
caoutchouc and mineral salts. The color may be absent, as in 
Oleander; whitish, as in Asclepias, Papaver, Hevea, and Apocynum; 
yellowish to orange, as in Celandine, or red, as in Sanguinaria. 
Chlor-zinc-iodine solution imparts to latex a wine-red color. 
The latex of the following plants is of value to pharmacy and 
the arts: 
Papaver somniferum and its variety album which yields Opium. 
That from the unripe capsules is alone used for this drug. 
Palaquium Gutta and Payena spp. which yields Gutra PERcHa. 
Hevea species, Ficus elastica, Landolphia species, Castilloa 
élastica, Hancornia speciosa, Forsteronia species, Funtumia elastica 
and F. africana, Manthot Glaziovit, Clitandra species and various 
species of Urceola and Euphorbia furnish most of the RuBBer of 
commerce. 
Lactuca virosa and other species of Lactuca yield the drug 
LacTuUcARIUM. 
Euphorbia resinifera, contains a white resinous latex which is 
gathered as the drug EupHoreium. 
24. EnzyMEs.—An enzyme or soluble ferment or unorganized 
ferment (according to Hepburn) is a soluble organic compound 
of biologic origin functioning as a thermolabile (sensitive to 
heat) catalyst in solution. Ostwald has defined a catalyst as 
an agent which alters the rate of a reaction without itself entering 
into the final product, or which does not appear to take any 
immediate part in the reaction, remains unaltered at the end 
of the reaction and can be recovered again from the reaction 
product unaltered in quantity and quality. The biologic 
catalysts (enzymes) differ from the inorganic catalysts in that 
they are sensitive to heat and light. They are destroyed quickly 
at 100°C. and most of them cannot be heated safely above 60°C. 
The optimum temperature range for this activity usually is 
from 40° to 45°C. Enzymes are soluble in water, dilute alcohol, 
glycerin or dilute saline solutions and are precipitated by con- 
centrated alcohol. They are colloidal and non-diffusible. 
They are.stimulated to activity by substances known as “‘activa- 
tors’ and their activity is checked by other substances called 
