and Laboratory Methods. 2649 



It is obvious that in the chamber E., and in the tubes F. J. K. and in the 

 flask M. the air pressure is the same, and will be registered on the millimeter 

 scale placed back of the open leg of the manometer. 



On this scale the reading is doubled, for the mercury falls in the closed as 

 much as it rises in the open arm, and the difference between the columns is the 

 sum of the rise plus the fall, or double the rise. 



Let us suppose our animal, preferably a young one, killed, the artery exposed, 

 and the ligatures in place ready for tying in the glass canula N. Let us sup- 

 pose the injection flask filled with 300 or 400 c. c. of normal salt solution heated 

 to 38 or 40° C, and the cork in place through which by means of a glass tube 

 connection between J, and M. is established. Now loosen the screw clamp at 

 O. just enough to let the 12-inch tube and the canula N. fill with the injection 

 mass and drive out all the air. Now cut the artery, insert the canula and tie it 

 in place. Then cut one of the large veins, say the inferior vena cava, to permit 

 the washing out of the vessels, turn on the water at the tap and loosen the clamp 

 at O. If only a little water is turned on, the water and most of the air escape 

 at G. and the air pressure remains very low. Even if the full water pressure is 

 turned on, if the escape at G. is too free, considerable air escapes that way and 

 the air pressure remains low. Therefore, when a good tiow of water is estab- 

 lished, gradually tighten the screw clamp at G., at the same time watching the 

 manometer ; the water begins to back up in the chamber E. escape for the air 

 at G. is cut off, and the air pressure rises. Thus a balance may be established 

 between the water pressure used and the air pressure. 



If the water in the chamber E. rises much beyond the openings D. D'., the 

 clamp at G. must be loosened a bit, or the water will back up into the tubes F. 

 K. J. and then over into the flask M. 



The limit of the pressure to be secured with this apparatus depends upon 

 the water pressure, which, however, is usually much greater than should be used 

 for injection. It is usually possible to get a pressure of 240 to 250 mm. mer- 

 cury, i. e., a 5 pound pressure, and as a rule one-fourth of this is sufficient. 



When the vascular system is well washed out by the normal salt solution, 

 clamp off the flow at O., turn off the water at the tap, pour out the remaining 

 normal salt solution, fill the flask as full as desired with the fixing agent heated 

 to 40° C., and again begin the injection. 



With this method any rapid fixer may be made use of. It is not always nec- 

 essary to wash out the blood vessels with normal salt solution. Fixation is usually 

 better, however, for having done so. With mercuric bichloride it does not so 

 much matter. With formalin and Hermann's fluid, however, it is advantageous 

 for fine fixation. The best fixers have proven to be mercuric bichloride, forma- 

 lin, Hermann's fluid, and alcohol. 



By this method the tissues, after a few minutes bath in warm normal salt 

 solution, are instantly penetrated to the last cell by the fixing agent. The 

 advantages are very great. The tissues, within a few minutes after anaesthetiz- 

 ing the animal (for anaesthetizing, illuminating gas is recommended as being 

 cheap, and causing no salivation), are perfectly fixed in a normal position, at 

 normal distention, apd during normal activity. The possibility of post mortem 



