SHEA AND LAWSON, ON POPULAR PHYSIOLOGY. 291 
gaged in microscopic investigations into the nature of those 
changes which go on in the tissues of the body, that they 
should make the knowledge they thus gain as practical as 
possible. Let them not be satisfied with the beauty or the 
interest of minute vital changes, but let them sirive to con- 
nect them with the great laws of life by which the population 
of the world is maintained and human health and happiness 
secured. Microscopical research is not an end, and the mi- 
croscope is only an instrument to help the eye to investigate 
the more minute phenomena of matter, in whatever form it 
presents itself. Of all the practical directions in which a 
fondness for microscopic research may be made available 
for the benefit of the individual who makes it, and for the 
circle in which he moves, is that of striving to understand the 
laws which regulate the healthful existence of his own body. 
The man who acquires any kind of knowledge at the expense 
of health has made a poor exchange, and the highest use to 
which human knowledge can be applied is to gain good health 
and length of days. As introductions to a knowledge of the 
great laws of life which are already known, we can recommend 
the manuals named above They differ in matter and style, 
but they have the same object in view. Dr. Shea’s is a plain, 
straightforward account of the phenomena of life, and is the 
result of much reading and reflection; Dr. Lawson is much 
more discursive, does not hesitate to introduce his own views 
of phenomena, and endeavours to amuse whilst he instructs. 
If we were asked for what class of readers they are adapted, 
we should say that Dr. Shea’s manual was best adapted for 
a class, whilst Dr. Lawson’s would be found more available 
for private reading and self-instruction. ‘ve will, however, 
endeavour to give our readers an idea of these useful little 
books by extracts from those portions of the books which 
treat of microscopical subjects. We first give an extract 
from Dr. Shea’s account of the blood. 
* BLoop-corPuscLes.—Two varieties of corpuscles exist, red and 
white. As seen under the microscope, they are flattened cells, of a cir- 
cular form, the red presenting either a bright or dark central spot, as 
they are brought in and out of focus. 
“ Red corpuscles are present in large numbers in the blood; their dia- 
meter varies from 3{,th to z)pth of an inch, and their thickness is about 
roth of an inch. When examined singly they appear almost colour- 
less, and it is only when viewed in numbers that they exhibit the florid 
colour. 
‘White corpuscles are much less numerous than the red, not more than 
one white to fifty coloured being present in human blood. As a rule, 
their diameter is greater than that of the red corpuscles, and may be 
estimated at g3gth of an inch. The form and appearance of the cor- 
puscles, both red and white, varies greatly, according to the character of 
VOL. III.—NEW SER. x 
