INTRODUCTION. 
THE CELL. 
Brotoey is that branch of science which investigates living 
organisms. What life is, we do not know, and consequently 
we cannot define it. We know that life can only exist 
when the temperature is between certain limits, and we know 
that the temperature of the earth at one time far exceeded 
the higher of those limits. Consequently, we know that life 
must have at some time or other originated on the earth, 
but how it originated we are quite ignorant, and the 
question of its origin is not properly included in the science 
of Biology. 
Notwithstanding these limitations, Biology is the most 
extensive field for investigation open to the human mind; 
not only does it investigate the structure and functions of 
plants and animals, but it also endeavours to find out why 
each particular plant and animal has its peculiar shape and 
structure, and how this shape and structure has been 
gradually attained. The more we study it, the more clearly 
we recognise the marvellous complexity of Nature. Just 
as ye ae unfolds to us the Infinite, and Geology the 
Eternal ; so does Biology unfold to us the Omniscient. 
Biology is divided into two branches—Botany, which 
is the study of plants; and Zoology, which is the study of 
animals—but the two meet on the debatable ground of the 
lowest living creatures, and Botany and Zoology are, in 
reality, but the study of the development in two different 
directions of the same substance—Protoplasm. 
B 
