W. A. TOOK, P. B. SPEILLER, H. SHERMAN, AND S. K. KLAUSNER 
203 
Figure 2. — Modified bobbin-like intrathoracic window showing screw thread and rigid removable cover. 
The use of the incident-light, dark-field sys- 
tem in conjunction with the modified thoracic 
window, permits microscopic study of the lung 
under truly physiologic conditions. We have 
minimized extraneous tissue motion, eliminated 
the need for the additional surgery required in 
transillumination techniques, and still provided 
the necessary light intensity for high magnifica- 
tion studies. We feel that this new system is a 
superior method for studying the pulmonary 
microstructure in the living animal. 
Our immediate objective in development of 
this model was to observe changes occurring in 
the pulmonary microcirculation of animals in 
shock. We have been frustrated in this objec- 
tive by the discovery of a number of factors 
which alter pulmonary blood flow other than 
shock. Accepting this diversion, we have studied 
these factors in order to have a more nearly 
normal model that will allow the discrimina- 
tion of the subtle charfges due to shock. 
Beginning with acute studies in open thoracic 
preparations we have found that exposure to 
air and drying will produce changes in the pul- 
monary capillary blood flow of normal animals 
after about one hour. This would seem to be 
the time limit for acute observations if they are 
to be reliable. 
In animals equipped with the thoracic win- 
dow a number of additional factors which alter 
pulmonary blood flow have been found. The 
flrst of these is rapid administration of normal 
saline. Infusion of physiologic saline equal to 
10% of normal plasma by a Harvard pump at a 
rate of 30 ml/min. will cause rapid aggrega- 
tion of erythrocytes and plugging of pulmonary 
capillaries by these aggregates. This phenomena 
is also seen in shock. Thus, careful attention 
