140 THE AMERICAN MONTHLY [May 
hand, after this primary increase they may be decreased 
and the proportion may be 1 to 800, Time of day is also 
a factor in producing variation. 
The instruments employed to-day for the examination 
of blood consist essentially of the microscope which is 
used to determine the quality and the character of the 
red and white cells, their comparative number and the 
presence of parasites ; the polariscope which is employ- 
ed in the color test for the purpose of determining the 
proportion of haemoglobin or in other words, the ability 
of the corpuscles to carry oxygen to the tissues, or for ex- 
ample,to detect the presence of carbon, mon-oxide-haemo- 
globin. Last but not less important is the so-called 
Thoma-Ziess haemocytometer, which is a very delicate 
instrument used to accurately estimate the number of cor- 
puscles in the blood. 
Anaemia, which means a deficiency in blood aad is rep- 
resented or portrayed by two conditions, in one of which 
the pallor and other symptoms are due to a diminution in 
the number of red corpuscles, while in the other there is 
a decrease of haemoglobin in each corpuscle. In regard 
to the white corpuscles, we can find even more interesting 
data, since their variation in number, form and character 
is marked in some diseases. Practically all conditions of 
the blood which are pathological, represent disease in or- 
gans connected with the blood directly or indirectly and 
do not depend upon primary changes in this liquid, ex- 
cept in rare instances, There are several varieties of 
anaemia, the most important of which is the so-called 
Pernicious Anaemia, in that it progressively gets worse 
until death occurs in the majority of cases, although a few 
may recover. The pathology of this disease is not un- 
derstood. It is characterized by marked pallor without 
loss of flesh, or to speak more correctly, the sub-cutane- 
ous tisues are added to rather than robbed of fat. There 
are gradually increasing dyspnoea, failure of strength, 
