THE BLOOD. 149 
visible to the unaided eye, while in the whole class of mam- 
mals they are very minute; their numbers also in this group 
are vastly greater than in 
others lower in the scale. 
The average size in man 
is zx457 inch (0077 mm.) and 
the number in a cubic mil- 
limetre of the blood about 
5,000,000 for the male and 
500,000 less for the female, 
which would furnish about 
250,000,000,000 in a pound 
of blood. It will be under- 
stood that averages only are 
spoken of, as all kinds of 
variations occur, some of ’ 
which will be referred to 
later, and their significance #1 14.—Thotograph, of cored ferbuscles of 
explained. ; 
Under the microscope the blood of vertebrates is seen to 
owe its color to the cells chiefly, and, so far as the red goes, 
almost wholly. Corpuscles 
when seen singly are never 
of the deep red, however, 
of the blood as a whole, 
but rather a yellowish red, 
the tinge varying some- 
what with the class of ani- 
mals from which the spec- 
imen has been taken. 
Certain other morpho- 
logical elements found in 
mammalian blood deserve 
brief mention, though their 
significance is as-yet a mat- 
ter of much dispute : 
Fic. 145.—Corpuscles from human subject (Funke). 1. The blood - plates 
A few colorless corpuscles are seen among the 
colored disks, which are many of them arranged (plaques,  hematoblasts, 
Beene third element), very small, 
colorless, biconcave disks, which are deposited in great num- 
bers on any thread or similar foreign body introduced into the 
circulation, and rapidly break up when blood is shed. 
2. On a slide of blood that has been prepared for some little 
