i? ZOOLOGICAL EXERCISES. 
Protoplasm is the only substance with which we ever. 
find life associated. It is a viscid, colourless, granular 
substance, in most cases containing a well defined dense’ 
structure called the nucleus. Its composition is not accu- 
rately known, but it is probably a combination of an 
albuminous substance, allied to protein, with a varying 
quantity of water, and it generally contains granules of oil. 
Living protoplasm is not stained by acetic extract of cochi- 
neal, but when it is dead it is stained. Iodine stains it 
brown, and an ammonaical solution of carmine stains it 
crimson. If heated with nitric acid, washed, and then 
treated with potash, it turns deep yellow. If treated first 
with copper sulphate and then with potash, it turns dark 
violet. It is dissolved by a solution of para and after 
some time by sulphuric acid. 
The composition of protoplasm is probably not constant ; 
like all organic nature, it is mutable and subject to change. 
Living protoplasm is distinguished from dead by exhibiting 
the power of spontaneous motion—that is, motion which is 
not owing to an external stimulus—assimilation and irrita- 
bility. 
Spontaneous motion.—This is exhibited in three forms. 
(1) Internal currents, by means of which the granules 
flow to different parts; (2) change in the external 
form; and (3) the rapid lashing backward and 
forward of minute hair-like processes of the pro- 
toplasm called cilia. These movements are accele- 
rated by weak solutions of alkalies and alcohol, by 
moderate warmth, and by weak induction currents ; 
but if these are increased in strength, all movement 
ceases. 
Assimilation.—Protoplasm is constantly decomposing, but 
it has the power of converting other organic com- 
