Gases of the Blood 617 



The cock d, placed on the slope of the inner lining of zinc, 

 allows urine or the condensed water to be extracted. Finally, in f 

 is a large orifice, which can either be closed by a screw-head, as 

 the figure shows, or allow the insertion of a thermometer, a serre- 

 fine with a handle, a cannula, etc. To prevent the air from escap- 

 ing around these instruments, they are put through a rubber ball, 

 (B. Fig. 34) held in a copper ring, whose screw thread closes it at 

 will. This arrangement, while completely shutting out the air, 

 gives the instruments a mobility which may be useful. 



When one wishes to see what is going on in the apparatus, he 

 puts a candle opposite one of the glass portholes, and looks through 

 the other; a dangerous proceeding, for it was under these conditions 

 that the explosion occurred of which I shall speak in another 

 chapter. 



The dog on which the operation is to be carried out is tightly 

 fastened, the nose held in a muzzle, on a framework of iron and 

 wood, whose form fits the inner wall of the apparatus, so that the 

 animal, once placed within it, cannot change its position. Into one 

 of its carotid arteries A is introduced a metal cannula S, which 

 can, when the animal is in position, be joined to a copper tube, 

 which screws through the wall of the apparatus, and is provided 

 on the outside with a cock R. 



These arrangements having been made, cock R is closed, and 

 the serre-fine SF is placed in the carotid, thus preventing the blood 

 from entering the cannula. Then the door of the cylinder is ad- 

 justed and the compression begun; it rises easily at the rate of 

 about one atmosphere every four minutes, when all the cocks are 

 tightly closed. It therefore takes about 40 minutes to reach 10 

 atmospheres, the maximum pressure which I have attained with 

 this apparatus. 



Nothing now is more simple than to extract the blood of the 

 animal, when the desired pressure has been reached. One needs 

 only to open cock R and remove the serre-fine SF to see the carotid 

 blood gush out with extraordinary force. In these conditions, in- 

 deed, the animal is like a sponge powerfully squeezed by a force 

 corresponding to 1.03 kilos, multiplied by the number of atmos- 

 pheres and by the exterior surface of its body. The whole proce- 

 dure then consists of fitting the glass syringe of Fig. 23 to the thick 

 rubber tubing which adheres to the cock. Opening the cocks with 

 precaution, one sees the plunger of the syringe raised vigorously by 

 the pressure of the blood. One must not fail to fit its own cock to 

 the syringe, and to close it immediately when one has secured the 



