372 



SCIENCE 



[N. S. Vol. LI. No. 1319 



Simple aseptic precautions are observed for 

 all operations. The forceps, knives, needles, 

 etc., for opening tlie shell are flamed before 

 using. The more delicate instruments used 

 for the operations proper are simply dipped 

 in alcohol and allowed to dry. The Eingers 

 solution and other fluids introduced into the 

 shell are boiled for a few minutes and allowed 

 to cool to 38° C. 



When the stage of operation is one in which 

 the amnion already surrounds the embryo, the 

 sac may be cut open and, after the desired 

 operation has been performed, it can be 

 " sutured " by pinching the edges together, 

 and will heal rapidly and completely. 



Various methods were tried for removing 

 portions of the embryo and the details of 

 these operations can not be given here as 

 they were modified for each particular set of 

 experiments. The electric cautery was tried 

 and abandoned because of the difficulty of 

 localizing the burn when the embryo is sur- 

 rounded by fluid. The method of cutting and 

 dissecting was the one most frequently em- 

 ployed. For dissecting away somites, spinal 

 cord, etc., steel needles groimd down to fine 

 points were used. For removing a more 

 prominent portion, such as the heart, the tail, 

 or a limb bud, iridectomy scissors proved to 

 be the most useful instrument. In removing 

 a blood vessel it was found advisable to inject 

 a small amount of Berlin blue, previously 

 boiled, directly into the vessel. This mate- 

 rial clumps on contact with the blood, stop- 

 ping the circulation and effectively plugging 

 the vessel and at the same time outlining the 

 vessel wall. The vessel can then be dissected 

 away rapidly, without causing hemorrhage. 



Mr. E. C. Albritton made use of electrolysis 

 for an extensive series of operations using a 

 needle and a pair of forceps connected by 

 wire to the two poles of a weak dry battery. 

 The needle is placed on the region to be 

 removed, and the forceps a short distance 

 away, in the fluid surrounding the embryo. 



After the operation a small window of thin 

 mica is flamed and placed over the opening 

 and sealed down with heated Gerlach's mix- 

 ture (beeswax 2 parts, lump resin 3 parts). 



The egg is then returned to the incubator. 

 The egg is turned so as to keep the window 

 at the side or below in order to prevent stick- 

 ing of the embryo to the jagged edges of the 

 shell. A ring of filter paper placed over the 

 exposed wax prevents its sticking to the floor 

 of the incubator. It is well to rotate the egg 

 slightly several times during the flrst few 

 hours after its return to the incubator. This 

 may be done automatically by a cradle rocked 

 by an attachment to an ordinary alarm clock. 

 If this is done the yolk remains freely 

 movable and the embryo can be brought 

 around under the window, when desired, for 

 observation. 



The method of keeping the air chamber im- 

 mersed in water at incubator temperature 

 during the operation has only recently been 

 adopted and it has greatly reduced the mor- 

 tality of chicks operated on at the age of 

 forty-eight hours and over. Formerly, when 

 the shell was opened, without this precaution, 

 the yolk always sagged away from the open- 

 ing and before the operation could proceed it 

 became necessary to add Ringer's solution, 

 drop by drop, in order to bring the embryo 

 back to the level of the opening. This usually 

 consumed more time than the operation 

 proper. On opening such an egg immediately 

 after the operation it is found that the air 

 chamber has been completely obliterated. 

 Evidently, this sagging away of the yolk from 

 the opening is caused by the gradual forcing 

 out of air from the air chamber. When such 

 an egg with the air chamber obliterated and 

 filled with Ringer's solution is returned to the 

 incubator it forms an inelastic chamber with 

 no room for expansion of the contents. Any 

 slight increase in temperature, in such an 

 egg, would seem to be sufficient, as a result 

 of the increased pressure, to cause embarass- 

 ment to the heart beat, in embryos in which 

 the circulation has started. Whether this is 

 the correct explanation or not, many chicks 

 died, when this method was used, within a 

 few hours after their return to the incubator. 



However, in the embryos in which the air 

 chamber is immersed diiring the operation, 

 almost no sinking of the yolk takes place 



