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CARNEGIE INSTITUTION OF WASHINGTON. 



In measuring the sitting height of small embryos, where it is desired 

 to obtain readings involving fractions of a millimeter, it was found 

 necessary to have some instrument more accurate than small calipers. 

 No matter how careful one may be, it is not always possible to so con- 

 trol the cahper points that they come in perfect contact with the ends 

 of the embryo without indenting them or without risk of injuring the 



Fig. 1. — Instrument for measuring embryos. X, Leitz No. eyepiece with cross-hairs; Z, 

 70 mm. Zeiss objective; Y, glass container for embryo; V, standard on top of which the 

 stationary plate of the Vernier scale is mounted. Reading is made from rear of instrument. 



specimen. The difficulties are increased by the fact that the measure- 

 ment has to be carried on under fluid. A special measuring microscope 

 was therefore devised (fig. 1) which has been found to adequately meet 

 the requirements. With this apparatus one can measure with accuracy 

 to 0.05 millimeter. For fetuses of the later months of pregnancy the 

 methods of measurement that have prevailed are quite unsatisfactory 

 and subject to considerable individual error. To meet this difficulty 

 a suitable apparatus has been designed by Dr. Adolph H. Schultz; 

 this is now in routine use in this laboratory and in the obstetrical 

 clinic of the Johns Hopkins Hospital. 



