663 
PROFESSOR H. N. MARTIN ON THE INFLUENCE OF VARIATIONS 
supply of fresh blood to the respiratory nerve centre. To complete the preliminary 
operation the inferior vena cava is tied above the diaphragm, and the right lung- 
being pushed towards the median line, the vena azygos is ligated near its junction 
with the superior cava ; the latter vessel is then tied below the point where the 
innominate and internal mammary veins join it by tightening one of the ligatures 
already described as placed loosely around it. 
The next step is to wash out the blood contained in the heart and lungs, and 
replace it by defibrinated blood. For this purpose the cannula 2 (Plate 48, fig. 3), 
connected with the Mariotte flask U, filled with defibrinated Calf’s blood at the 
temperature 38° C., is inserted into the cardiac end of the superior cava, and tied 
there. The clamp on the tubing connecting the flask with the cannula is opened, and 
blood from the flask allowed to enter the right auricle. The clamps on each carotid, 
and on the aortic cannula, are then opened in turn for a short time so as to wash out 
all blood already in heart and lungs, and replace it with the defibrinated blood. 
This having been done, and the clamps again closed, the animal, still tied on the 
dogdiolder, is transferred to the warm moist chamber represented in outline in 
Plate 48, fig. 1 ; in this chamber it is thenceforth fed steadily with defibrinated blood of 
known temperature, supplied at a known and controllable pressure, and from the 
chamber it pumps out blood against a known and readily varied aortic resistance. The 
structure, contents, and preliminary preparation of the warm chamber have next to 
be described. It is 125 centims. long, 65 centims. wide, and 65 centims. high. It 
has no bottom, but when in use sits in a shallow iron trough (not represented 
in the figure) filled with water, and raised on supports which admit of Bunsen 
burners being placed under it, by whose means the air in the chest is kept moist 
and warm. The roof, sides, and the end, A, are glazed; the end, B, is of wood, 
and perforated by apertures through which several tubes pass. The object of 
glazing most of the walls of the chamber is to enable a ready view to be had of what 
is going on inside it; this is apt to be interfered with by condensation of water on 
the glass during the course of experiment; this drawback may, however, be nearly 
entirely obviated by smearing the inside of the glass with glycerine. 
In the chest are two Mariotte’s flasks, C and D, each of a capacity of about 
four litres. The flasks are entirely similar in all respects, but for the sake of 
clearness in the diagram the tubes only have been represented in connexion with C, 
while the water-jacket which surrounds each flask is only indicated with D. This 
jacket, E, is merely a cylindrical tinned-iron bucket, somewhat wider than the flask. 
It is filled with water, and has, in connexion with it, a syphon by which it can be 
readily emptied, and a supply tube through which it can be filled. The syphon and 
supply tube have been omitted in the figure. Their ends pass outside the warm 
chamber, so that the water in the jackets can be changed without opening the box. 
As the flask empties of blood when in use, it tends to float up in the water of the 
Ij 
