tA 
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parts which have the same function, as for instance the villi of the 
intestine, glomeruli of the kidney or lobule of the liver. Each of 
these parts has a distinct relation to the blood-vessels so that if the 
relation is known for one it is practically known for the whole organ. 
The aim of the present study has been to find the relation of 
the blood-vessels to the lobule of the lung. All persons who have 
already investigated this organ know that in it there are special 
difficulties to be overcome, and in my investigations I have employed 
all the ordinary methods of study as well as that of reconstruction. 
The latter gave the most valuable results. It showed that the air- 
passages of the lobule were far more complicated than anticipated 
and that this knowledge was absolutely essential before the blood- 
vessel could be interpreted properly. 
The following methods were found to be of the greatest value: 
1) Injecting the lung with air or illuminating gas and then allow- 
ing it to dry. 
2) Corrosion preparation in wax or in Woop’s metal. 
3) Digestion in pepsin after the air-passages and blood-vessels 
had been injected with colored celloidin. 
4) Reconstruction as well as free-hand modeling. 
The first method is of greatest service in the study of the lungs 
of Amphibia and Reptilia. In these animals the large air-sacs permit 
a very careful study of the interior of the lung after it has been 
blown up, dried and cut upen. The mammalian lung, however, is hard 
to dry, and the best specimens are of little value in the study of 
the finer structure. 
Injections with wax and with Woon’s metal proved of great value 
in the study of the blood-vessels, but are of little value in the study 
of the air-passages within the lobule. It is of great service to study 
the bronchial tree of embryos which are sufficiently advanced to permit 
a cannula being tied in the trachea. But all that can be obtained 
with Woon’s metal or with wax can be obtained equally well or better 
with celloidin. It is by all odds the most desirable method. The 
celloidin is to be colored with vermillion, Prussian blue or chrome 
yellow. After the vessels have been injected the organ may be placed 
in water for some time and then the tissues are digested with pepsin 
and one half per cent hydrochloric acid. For this latter procedure 
I am under obligations to Dr. MıxTEr of;Boston. The digestion, of 
course, takes place best in the thermostat and when the tissues are 
thoroughly softened, which often takes days, they are to be washed 
off in flowing water. In all cases I found that the corrosions are 
