their business.  Sir Francis Hopwood, in laying down these regulations, gave emphatic warning “that in case any manufacturer, importer or dealer came under suspicion his permits should be immediately revoked.  Reinstatement will be slow and difficult.  The British Government will cancel first and investigate afterward.”  Of course the British had a right to say under what conditions they should sell their rubber and we cannot blame them for taking such precautions to prevent its getting to their enemies, but it placed the United States in a humiliating position and if we had not been in sympathy with their side it would have aroused more resentment than it did.  But it made evident the desirability of having at least part of our supply under our own control and, if possible, within our own country.  Rubber is not rare in nature, for it is contained in almost every milky juice.  Every country boy knows that he can get a self-feeding mucilage brush by cutting off a milkweed stalk.  The only native source so far utilized is the guayule, which grows wild on the deserts of the Mexican and the American border.  The plant was discovered in 1852 by Dr. J.M.  Bigelow near Escondido Creek, Texas.  Professor Asa Gray described it and named it Parthenium argentatum, or the silver Pallas.  When chopped up and macerated guayule gives a satisfactory quality of caoutchouc in profitable amounts.  In 1911 seven thousand tons of guayule were imported from Mexico; in 1917 only seventeen hundred tons.  Why this falling off?  Because the eager exploiters had killed the goose that laid the golden egg, or in plain language, pulled up the plant by the roots.  Now guayule is being cultivated and is reaped instead of being uprooted.  Experiments at the Tucson laboratory have recently removed the difficulty of getting the seed to germinate under cultivation.  This seems the most promising of the home-grown plants and, until artificial rubber can be made profitable, gives us the only chance of being in part independent of oversea supply.

There are various other gums found in nature that can for some purposes be substituted for caoutchouc.  Gutta percha, for instance, is pliable and tough though not very elastic.  It becomes plastic by heat so it can be molded, but unlike rubber it cannot be hardened by heating with sulfur.  A lump of gutta percha was brought from Java in 1766 and placed in a British museum, where it lay for nearly a hundred years before it occurred to anybody to do anything with it except to look at it.  But a German electrician, Siemens, discovered in 1847 that gutta percha was valuable for insulating telegraph lines and it found extensive employment in submarine cables as well as for golf balls, and the like.

Balata, which is found in the forests of the Guianas, is between gutta percha and rubber, not so good for insulation but useful for shoe soles and machine belts.  The bark of the tree is so thick that the latex does not run off like caoutchouc when the bark is cut.  So the bark has to be cut off and squeezed in hand presses.  Formerly this meant cutting down the tree, but now alternate strips of the bark are cut off and squeezed so the tree continues to live.