160 TEXT-BOOK OF EMBRYOLOGY. 



embryos are often extremely valuable, for many anomalous conditions in postnatal life 

 can be explained on the ground of unnatural developmental conditions. Obstetricians and 

 gynecologists can render great service to embryology by saving curettings or the entire uterus 

 in cases where pregnancy is suspected or known to occur and turning them over to a com- 

 petent embryologist. The earliest stages are especially valuable. Never should a human 

 embryo, normal or abnormal, under any circumstances be thrown away. 



When the uterus is removed where there is suspected pregnancy, it should always be saved. 

 Within as short a time as possible, carefully open the uterus by a ventral median incision. 

 If pregnancy has gone beyond the first month, the membranes and embryo are easily seen. 

 During the earliest stages of pregnancy, especially during the first part of the first month 

 it is sometimes very difficult to locate the embryo in the uterus. The most likely position 

 is on the dorsal wall. It may show only as a scarcely visible elevation in the mucous mem- 

 brane. If the little elevation is once recognized, cut out the block of uterine wall containing 

 it. Fix the block in some good fluid, such as Orth's fluid and embed carefully in paraffin. 

 Cut serial sections at right angles to the inner surface of the uterine mucosa. The sections 

 may be stained as desired, Weigert's hematoxylin and eosin giving good results (see 

 Appendix) . The most valuable human embryos in the earliest stages have all been obtained 

 in a similar manner. 



Embryos three to eight weeks old may be fixed with the membranes intact. Put the 

 specimen in a large quantity of strong alcohol (the alcohol of druggists is never too strong) . 

 The volume of the alcohol should be at least ten times the volume of the specimen. A 4 

 per cent, solution of formalin (one volume of the commercial formalin — which is a 40 per 

 cent, solution of formaldehyde gas in water — to nine volumes of water) may be used if alcohol 

 cannot be obtained at once. The specimen should not be left in formalin, however, longer 

 than a few days, for it is likely to become somewhat blackened owing to changes in the blood. 

 As soon as possible, it should be put in Orth's fluid for a day or two, and then put through 

 graded alcohols up to 80 per cent. Kleinenberg's mixture is also an excellent fixative for 

 young embryos. 



In embryos eight to twelve weeks old the membranes should be opened before 

 fixing. Strong alcohol may be used as a fixative, as in the earlier stages, but usually causes 

 considerable shrinkage. A better plan is to put the embryo in Orth's fluid for a few 

 days, the length of time depending upon the size of the embryo, and then to put it 

 through the graded alcohols up to 80 per cent. As mentioned in the preceding paragraph, 

 4 per cent, formalin may be used as a fixative, but should be followed in a few days by Orth's 

 fluid and the graded alcohols. Zenker's fluid is frequently used as a fixative for embryos 

 but always causes some shrinkage. Aside from the shrinkage, it gives very good results. 

 (See Appendix.) 



If embryos of twelve weeks or more are to be studied histologically, they should be 

 opened by a ventral medial incision before fixing. It is well also to make a few incisions 

 in the skull. If it is desired, organs or parts of organs may be removed and fixed by them- 

 selves. Orth's or Zenker's fluid may be used with good results. 



For gross preparations, embryos may be fixed as suggested in the preceding paragraphs. 

 Then, if occasion requires, they can be studied histologically at a later period. Gross 

 preparations which are not likely to be used histologically can be fixed and preserved indefi- 

 nitely in 4-10 per cent, formalin, with practically no shrinkage, although there is a possi- 

 bility of discoloration due to changes in the blood. 



As complete histories as possible of all embryos should be obtained and recorded. The 

 younger stages should always be carefully measured before fixing. It is also advisable to 



