CH. XI] 



MODELS FROM SERIAL SECTIONS 



411 



Further, the difficulty of getting a true conception of the object 

 by studying only two dimensions in the sections is very great; hence 

 a model giving all three dimensions becomes almost a necessity for 

 the beginner in embryology, and is of enormous advantage to an in- 

 vestigator in working out the true form and relation of complex 

 structures. For modeling a series it is of great advantage to have 



A B 



FIG. 244. DRYING OVEN FOR SLIDE TRAYS. 



(From the Anatomical Record). 



A The oven showing all the parts, the oven proper (j) is lifted up to show the 

 electric lamps in the base (2). 



B Sectional view of the oven (/) and base (2) showing the construction and 

 the air currents. One tray (5) is in position. 



A The asbestos lining of the outer shell. B One of the numerous ventilating 

 holes. C Flue for the escape of air. H Runs for the slide trays. 



D Door of the support or base (2). W-L Wiring for the lamps. One can 

 vary the heat by turning out one or more of the incandescent bulbs. 



photographs of the object to be modeled. If possible the object 

 should be photographed in the fresh state and after fixation. The 

 more aspects photographed the better. 



The principles involved in the construction of a model are exceed- 

 ingly simple: 



1. It is necessary that the embryo or other object to be modeled 

 should be cut into a series of sections of definite thickness. 



2. The sheets of modeling material must be as much thicker than 

 the sections as the model is to be larger than the original. 



