166 VEGETABLE PHYSIOLOGY 
protein and all of them are extremely difficult to prepare in 
a pure condition, too much stress must not be laid upon 
the results obtained. These, moreover, are, as we should 
expect, not altogether concordant. 
Analysis of a crystallised protein prepared from the 
seed of the hemp showed it to have the following percentage 
composition, which may be taken, within somewhat wide 
limits to be fairly typical of all :-— 
Carbon ; ‘ ‘ . 51:58 
Hydrogen . i : ‘ 6°88 
Nitrogen. , ‘ . 188 
Oxygen : ‘ 3 . 21°65 
Sulphur ‘ ‘ : : 1:09 
Besides containing these essential constituents, many 
proteins leave on ignition a certain amount of ash. This 
consists of small amounts of the chlorides, phosphates, sul- 
phates, and carbonates of sodium and potassium, with traces 
of the corresponding salts of calcium, magnesium, and iron. 
It is not certain that these ash constituents are an integral 
part of the protein molecule in any case; the balance of 
evidence points rather to their being impurities which are 
very difficult of removal. 
Most of the proteins found in plants exist in an amor- 
phous condition, and are very closely incorporated with 
the protoplasm. In a few cases they are met with ag 
definite grains, and in certain reservoirs of food material 
they occur as crystals. Some of them can be made to 
erystallise after extraction from the organism, but many 
forms exist which do not possess this property, so far as 
we know at present. It is not certain, however, that the 
crystals are always composed of pure protein only. 
The proteins vary very much among themselves as to 
their solubility in water and other neutral fluids. Some 
are soluble, others insoluble, in water ; some are soluble only 
in solutions of neutral salts of various degrees of concentra- 
