122 THE AMERICAN MONTHLY. [July, 
statement that the careful treatment, as planned above, will not, to any sensi- 
ble extent, damage the cells. But as the learner becomes a skilled and original 
student, whenever he attempts any new departure he must guard himself very 
carefully against difficulties from this source. Accepting, then, that appear- 
ances have not been made unnatural by the processes of preservation, imbed- 
ding, and so forth, let us go on to the reconstruction, in imagination, of the 
green gland from them. 
a. Shape of the cells of the alveolus.—Study of these cells will soon 
convince one that seen in section they are squarish. To this conclusion he 
will be led by two considerations; in the first place he will here and there 
find one side wall or perhaps both very distinctly visible, and where he can 
find this the squarish outline of the cell will be plain enough. Then, sec- 
ondly, wherever he finds the wall and the nucleus, which he judges to belong 
to the same cell, he will find them a certain distance apart. This will help 
to guide him where to look for the wall of the other side, and direct him to 
search there even more carefully, and perhaps detect it. In this way, by 
careful observation, and at the same time with comparison of the results of 
the same methods applied to the study of the alveolar wall in a score or two 
of places, the observer soon satisfies himself that a cross-section of the cells 
is truthfully represented in figure 3 or figure 2, though the actual appear- 
ance at first sight is shown in another part of figure 2. | A figure which thus 
represents the facts as they are believed to be, not on a foundation of mere 
guesswork, but after diligent study, is usually called a diagrammatic repre- 
sentation, and a diagrammatic representation, when conscientiously made, 
is evidence that the observer has both seen, and compared, and judged. 
Such figures are common in our text-books; they do not often look like our 
sections, for they are somewhat more ideal than any particular section is 
ever likely to be, but they are all the more helpful on that account. 
Having thus decided the shape of the cell in cross-section, we must go still 
further, and determine its shape asa solid figure. To accomplish this the 
most natural thing would be to turn it up and look at its side. This, how- 
ever, we cannot do with the cells whose cross-section we have already 
inspected. We can, however, cut part of the gland in one plane, and the 
rest in the plane at right-angles to the first, which would give the desired 
section, and find other alveolar cells cut in the other direction. This is the 
true way to do, and one should make a practice of slicing all tissues in two 
planes, so that he shall cut lengthwise and crosswise of all cells. In the case 
of the green gland the cells would look the same in any section which was 
vertical to the basement membrane, and, as the cubical form only could give 
squares in any section, the inference is necessary that the green-gland cells 
are cuboidal bodies. This conception of their form will be corrobor- 
ated by the study of the nucleus, the cells being so small that section is about 
the thickness of each one. They can be cut much thinner, so that cells will 
be seen without the nucleus. Such would be more frequent if the cells were 
a prism, and the nucleus globular and in the centre. Therefore, though one 
cannot by this mode of study see all of any one cell, he can find enough ap- 
pearances to put together to assure himself of the rightness of his conclusion 
that the cells are cubes.* 
The inspection of the section will reveal the fact that there is more than 
one kind of alveolar lining cells, and while the form just described and 
shown in figure 2 is to be found lining some of the cavities, in other places a 
* Before leaving this part of the subject I will say that there is a method of cell-study which proceeds upon an 
entirely different plan from the one we are at present following, namely, by isolating the cells by the dissolving 
of the substance which cements them together, thus setting them free, when they may be studied in their entirety. 
This method should supplement the method by section, and will be described at a future time. 
