EXTRACTS FROM FOREIGN JOURNALS. 127 
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(c) I have observed some eight or ten times, and always by 
;hance, the thickness, resistance and complete imperforation of 
he mediastinum upon cadavers in which not the slightest care 
lad been taken to prevent the laceration of the mediastinum. In 
liese horses, the mediastinum had, without exaggeration, the char- 
icters of solidity and of homogeneity equal to those of the mesen- 
;ery itself. 
(d) In observing attentively the posterior mediastinum upon 
he cadaver, after making a large opening in the thorax, on the 
ame side, and after raising the lung to expose it, the openings 
>f the mediastinum are seen increasing more and more in size 
md in numbers, and after a short time the membranes will have 
he appearance of a delicate piece of lace; something very dif- 
erent from that which it first presented. These successive lacer- 
itions are due to the abnormal tractions put on the septum under 
he influence of the flabby condition of the lung, and the relax- 
ition of the diaphragm after the opening of the thorax. 
This fact leaves no doubt as to the true nature of the medias- 
inic perforations described by authors as constituting their nor- 
nal condition. Is it not sufficient to prove their purely acciden- 
al character ? 
(e) But, it is easy to observe de visu , the formation of these 
>erforations. For this purpose let the two pleural sacs be opened 
hnultaneously and with great care, by tubes with facettes, pre¬ 
viously secured in the upper part of an intercostal space, similar 
>n both sides, and then allow the air to enter very slowly, and 
’ ery often the mediastinum will be preserved intact. Then ob- 
erve carefully and with a magnifying lens the serous surface. 
It first very small openings will be observed, but these will by 
legrees increase. Evidently the success of this experiment will 
r ary according to the delicate condition of the membrane. In- 
leed, in some instances, this is so much the case that the perfora- 
ions are already formed, when the lung is raised to expose it. 
2d, Histological Examinations. —What has just been ob- 
erved with the magnifying lens is confirmed by microscopical 
| lamination in a very positive manner. 
The mediastinum being carefully exposed from both sides of 
