Taking large and small together--and allowing for waste, the heads and tails that would have to be chopped off--Karl calculated that he would get nearly a square foot each out of the eels; and that about five hundred skins would make the balloon bag.

But as they would have to be cut occasionally with a slant, in order to get the globe shape, perhaps a few more would be needed; and therefore Ossaroo was to keep his baits in the water, until the requisite number of eels should be hooked out of it.
Ossaroo had another department assigned to him besides catching the fish; and one that took up more of his time: since the baiting of the hooks, and looking after them, required only his occasional attention.
Spinning the thread by which the skins were to be sewed together, was a much more delicate operation: since in these both strength and fineness were absolutely necessary.

But as Caspar had said, Ossaroo was an adept with the distaff; and several large skeins of the finest twist were soon turned off from his nimble fingers.
When enough thread had been thus produced, Ossaroo proceeded to making the cords and stronger ropes, that would be needed for attaching the "boat"-- as well as to hold the balloon in its place, while being got ready for its ascent.
Caspar's employment was--first, the skinning of the eels; and afterwards the scraping, boiling, and drying of the skins; while Karl, who acted as engineer-in-chief, besides giving a general superintendence to the work, occupied himself in imparting the final dressing to the material, and cutting it into such shapes, that it could be closely and conveniently stitched together.
Karl had also made an excursion into the forest, and brought back with him large quantities of a gum, which he had extracted from a tree of the genus _ficus_--a sort of _caoutchouc_--which is yielded by many species of _ficus_ in the forests of the Lower Himalayas.

Karl had gone in search of this substance, because he knew it would be required for paying the seams, and rendering them air-tight.
When they had pursued their various avocations for about a week, it was thought that material enough of every kind was collected and made ready; and then Ossaroo was set to stitching.

Fortunately, they were provided with needles: for these had formed a part of the _accoutrement_ of the plant-hunters--when originally starting upon their expedition.
As neither Karl nor Caspar had any experience in handling such sharp tools, the sewing had all to be done by Ossaroo; and it took another full week to accomplish this Sartorean task.
At the end of that time, it was fully accomplished and complete; and the huge bag was ready to receive its coat of gum varnish.