(.21 ) 
PROGRESS OF MICEOSCOPICAL SCIENCE. 
Have the Lungs on their ultimate Alveoli Squamous Epithelium ? — 
This question has been often asked for the past thirty years, and has 
been answered both in the affirmative and the negative. However, 
now a Mr. Henry Brown, of Northallerton, seems to have decided the 
question. In a letter to the ‘ Lancet,’ cf Nov. 7th, 1874, he says of 
this question that “ when we find such men as Waters, Kolliker, 
Rossignol, Ebertli, Hirschmann, and Arnold advocating its presence, 
and Rainey, Todd and Bowman, and Zenker denying its existence, 
what are we to say? With your permission I shall briefly point out 
how the examination of the pulmonary tissue should be conducted, 
and I shall explain how I and others have failed to observe the 
epithelium, and how by a little careful attention and manipulation 
any person possessing a good microscope may, with great ease and 
facility, demonstrate its existence. Reasoning from analogy, I con- 
sidered the ultimate lung tissue could not be an absolutely bare and 
structureless membrane, upon the walls of which the capillaries 
ramified. Accordingly I obtained some lung tissue from a recently 
killed pig, and examined it after the least delay possible. I excised a 
portion from the thin edge of the lung, and, placing it over the index 
finger of the left hand, made slight pressure upon its upper surface, 
and then seized it with the thumb and middle finger of the same hand, 
so as to secure it firmly, and by means of fine curved scissors snipped 
off small pieces. My object in so doing was to make the pieces as 
thin as possible, and I have found this mode of procedure preferable 
to any other. The thin pieces of lung were washed in distilled water 
for about fifteen minutes. I used a deep watch-glass for this purpose, 
and by means of two needles I was able to wash the pieces most effec- 
tively. I then transferred the small pieces of lung to another watch- 
glass containing some distilled water, and, after stirring them about 
for a minute or so, I found that very few air-bubbles made their 
appearance ; and taking up a small piece of lung, transferred it to a 
glass slide, and placed upon it a thin glass cover. This I carefully 
examined under a power of 310. The appearance was different from 
what I had before seen, and I resolved to apply a very weak acetic 
acid solution. For this purpose I added ten drops of glacial acetic 
acid to one ounce of distilled water, and, by means of a Clark’s 
stopper, allowed a drop to pass between the cover and glass slide. 
The effect was truly charming. Beautiful epithelial scales with a 
nucleus presented themselves. The reason why I have formerly been 
unsuccessful in demonstrating the epithelium of the alveoli of the 
lungs is this : that the acetic acid employed was too strong, and 
immersion of lung tissue in moderately strong acid causes disintegra- 
tion and solution of the epithelium. I think, Sir, this point should 
now be finally settled, and I shall most willingly send further par- 
ticulars to any person interested in this vexed question. I have 
carefully measured the epithelium, and observed its disposition, and 
