s laid, a chemical change begins to take place, and more
or less gas is formed. This gas finds its way to the large end, and as
the decomposition increases the egg becomes lighter at the heavy end,
and finally enough gas is evolved to bring it to the surface."

[Illustration: _Fig. 15._ TESTING EGGS]

The most important work on hand was the construction of the addition to
their home. After considering the matter in all its details, it was
concluded to put up a building entirely separate from the other
structures, to contain four rooms, one of them to be large and utilized
as a common living room, and the others as sleeping apartments.

The material had been taken out for the building, and the Professor,
John, George and Ralph were engaged at this work, while Harry and Tom
were engaged in the machine shop and were busy in turning out the
barrels for new guns, as well as preparing the ammunition.

The tools in the machine shop were not numerous enough to advantageously
utilize more of them there, and the building was now very important to
them, as the four boys were compelled to sleep in the shop, for want of
room in the house.

The joist had all been laid for the lower floor and the studding now
being put up and the upper joist laid on preparatory to erecting the
rafters. John was an expert in building, and was really the directing
hand at the various steps in the operation. While engaged in the drawing
up of the rafters, one of the floor pieces gave way, and John was
precipitated to the floor below, striking as he fell one of the lower
joist, which cut a terrible gash in his head and rendered him
unconscious.

The Professor rushed over to the fallen man, and the boys were on the
spot to render assistance. Chief, who was also an interested worker, was
the first to grasp him with his powerful arms, and disdaining the
assistance of the others, carried him to the house and gently laid him
down, as the Professor directed.

Without a word he rushed for the jar of water and brought it to the
Professor, who bathed his wounds, but the blow was so severe that he
exhibited no signs of returning consciousness.

Harry and Tom rushed over to the house in consternation, and exhibited
the greatest grief.

"Do you think he has been badly hurt? Do you think it is fatal?"

"It is still too early to determine that. See this wound? It was a
terrible blow. As it is, directly above the ear, it may not be as
serious as if he had be