102 THE AMERICAN MONTHLY [June, 
spaces also always lead from the centre toward the outside of the gland, and 
they lead by openings through the sack, J, which envelopes the gland, to the 
body space, in which the gland itself les. The blood space is shown in fig. 
2, and at g. m. the gland sack and the position of the blood space (b.c.) are 
shown. 
6. The blood corpuscles.—Scattered through the blood spaces in all 
parts of the gland (e. g., fig. 3) one may see small globular bodies, the blood 
corpuscles. ‘The presence of these may be taken as demonstrating the con- 
tinuity of the blood cavity, even into the places where the walls of the gland 
cavities are in immediate contact, and justifying the inference that these walls 
are only temporarily pressed against each other. The corpuscles are all alike 
in appearance, except some slight variations as to size. Each one exhibits an 
outer thin coat, which is hardly distinguishable from the very deeply-staining 
substance making up the mass of the corpuscle. Each corpuscle is regarded 
as acell. The substance of the cell is not homogeneous, that is, of even tex- 
ture throughout, but is made up of portions mixed together very closely, but 
some of fen staining much more deeply than others. About six of the cor- 
puscles, laid side by side, would measure one one-thousandth of an inch ; ; the 
corpuscle is, therefore, about ;,;, of an inch in diameter. The corpuscles 
always seem circular or oval in all parts of all sections. What are we to say 
as to their real shape? In studying sections the student must keep constantly 
in mind that in sections he is not dealing with objects as he deals with objects 
of natural vision. In microscopical study there is very little or no perspective ; 
a cylinder or a sphere may look the same in section, and this fact must be con- 
stantly kept in mind in interpreting one’s observations. Bearing this in mind, 
shall we think the corpuscles to be globules or the cut ends of cylinders? The 
question may be settled, of course, by study of the blood of the cray-fish from a 
fresh specimen in a film, after the usual manner. This would be final, and, at 
the same time, an easy method. A second method would be to cut sections 
in various planes. This method must be applied to the study of some tissues. 
It would show the corpuscles of the same shape in every plane, and hence 
spheroidal bodies, the only rounded bodies which can have the same shape 
in any section. 
The name for the substance of the corpuscle is protoplasm. What it is, 
chemically, does not concern us at present, but microscopically, protoplasm 
presents certain characteristics which are met with here, as in all living cells, 
some of which we must note. Protoplasm in animal or vegetable cells, so 
long as it is alive, does not stain readily. But as soon as it is killed, we can- 
not say before it has undergone any change, but we believe before it has 
changed greatly, a great variety of reagents affect it in ways which the his- 
tologist uses to help him in his studies upon it. For one thing it is very 
deeply colored by various dyes, as logwood or carmine or the anilines. When 
so colored it never has a clear, transparent look, but an opaque, or, at least, 
translucent, look, and may be coarsely g aenbloke with some granules densely, 
and others faintly, stained, or it may he very coarsely granular. The sub- 
stance of the corpuscle hos the appearance of a densely granular protoplasm 
deeply and very thoroughly stained. While speaking ow protoplasm as stain- 
ing thus, we must notice that many other substances which will dye with 
the proper dyes do not look like this cell substance. Thus fat, starch, and 
horn may be mentioned as three which, if present in the free state in the © 
green gland in any quantity, could be told from the protoplasm merely by 
their different reactions toward staining fluids. I mention these matters to — 
enforce the importance of noting well the appearance of the substance within 
the corpuscle. We shall later. meet with cells which contain something 
besides protoplasm. 
