ClI. VIII] rilOTO-MlCROGRAPHY 213 



Finally when the embryo is cut into serial sections and 

 mounted, a picture of the whole embryo should accompany the 

 series. 



285. Size of the Pictures. For all embryos it is well to 

 make one picture natural size ( X i ) and then for the smallest ones 

 a magnification of at least five times natural size (X 5). Here, as 

 with the magnification of the microscope, linear magnification is 

 always meant ( 170, 171). 



286. Objectives. For making pictures from one to five 

 times natural size objectives of 60 to 100 mm. focus answer well 

 (Figs. 166-167). Short focus (75 to 100 mm. equivalent focus), 

 wide angle photographic objectives are also admirable for this work. 



>; 287. Record of Negatives. As indicated in 276-278 each 

 negative should have a record, see record blank ( 316). On the 

 negative itself should be also written the main facts with carbon ink. 

 The name and magnification, date and any other details which may 

 be thought desirable can be put on the envelope containing the nega- 

 tive and then stored like a catalog card as described above ( 278). 



S 288. Photographing Large Transparent Objects. 

 There are many large transparent objects which it is desirable to 

 photograph, e. g., chick embryos mounted whole, large sections of 

 organs like the brain, etc. These must be photographed at a low 

 magnification. 



Successful photographs require an even lighting and an objec- 

 tive which has sufficient field to take in the whole object. The 

 camera used for embryos (Fig. 182) may be used in connection with 

 the projection microscope condenser. For very large objects or for 

 large pictures the vertical camera (Figs. 161, 169) is reversed in 

 position on the supporting frames, and elevated only sufficiently to 

 make a sky back-ground ; or a 45 degree reflector of white cloth or 

 paper of sufficient size must be used fora horizontal camera. If one 

 has the earth for back-ground the light will be dull and uneven 

 and a very long exposure is necessary, and the final results 

 unsatisfactory. 



289. Use of the Special Microscope Stand. In order to 

 hold the specimen in position and to focus it accurately, it is put on 

 the stage of the special microscope stand (Fig. 165), which is 



