Dia HERBERT G. WILLSON 
while the other was a child whose age could not be definitely 
ascertained, but was certainly less than thirteen years. In the 
ease of the adult, portions of suitable size were taken from the 
lungs and immersed in Bouin’s fluid, but in the case of the child’s 
lung the entire organ was first injected through the bronchus 
under gentle pressure with Bouin’s fluid, and then immersed in 
the same fluid, portions suitable for sectioning being taken only 
after the tissue had been fixed in this manner. The portions 
selected were carried through the various grades of aleohol and 
imbedded in paraffin, and to secure satisfactory penetration 
of the paraffin they were, while in 70 per cent alcohol, placed 
under the bell-jar of an air-pump and the air exhausted till 
bubbles ceased to rise from the cut surface of the tissue. 
By this method a perfect infiltration of the paraffin was ob- 
tained, and the tissue was cut into serial sections, 204 thick in 
the case of the adult lung and 30. in that of the child. Both 
series were stained with Weigert’s elastic tissue stain, this being 
chosen with the intention of studying later the distribution of the 
elastic fibers in the human lung. Wax reconstructions of the air 
spaces, ie., negative reconstructions of portions of each lung 
were made at a magnification of 100. To ensure accuracy in the 
superposition of the wax plates in the model of the adult, numer- 
ous bridges were left in cutting out the air-spaces, but in the 
second model the necessary accuracy was obtained by the use of 
a duplicate series of drawings of the sections made upon trans- 
parent paper. A duplicate drawing of a section about the middle 
of the series was covered by a sheet of glass, and on this the pieces 
of wax representing the corresponding air-spaces were placed 
one after the other, as they were cut from the wax plate. The 
next succeeding drawing was then carefully oriented upon that 
first chosen, so that the position of the air-spaces shown in the 
one could be accurately determined with reference to those of the 
other, and from the information thus obtained the pieces of 
wax representing the air-spaces of the second section could be 
accurately adjusted on those cut from the first plate. Dealing 
in this way with successive drawings and wax plates, half the 
model was built up. This completed portion was then detached 
