1+20 EXPERIMENTAL CHICK EMBRYOLOGY 



Botatlon of the esffa : The hen generally turns the eggs frequently. This is not 

 necessary for the first day or two hut thereafter all eggs should be turned at least twice 

 daily in order to prevent adhesion of the membranes, dotation of operated eggs will, of 

 Course, be limited. 



The candling of egga : Incubation time is not an accurate criterion of ontogenetic 

 age so that It is necessary to provide a device for sending light through the blastoderm 

 so that its age can be approximated by direct observation. The mail order houses offer 

 inexpensive candling equipment but it is very simple to make one. Fasten a light socket 

 to a board; place around the socket a large tin funnel cut to fit, which acts as a reflec- 

 tor; invert over the 100 watt bulb a small waste basket through the bottom of which is cut 

 a circular hole; fasten beneath the hole a piece of coarse wire gauze, somewhat depressed, 

 to cup an egg; cover the hole (outside of basket) with a heavy felt cloth (to cut out 

 extraneous light) and cut a slit in its center slightly shorter than the length of the 

 average egg. A switch may be provided for the light, fastened to the base board. The 

 entire cost should be about 50 cents. The egg is placed over the slit in the black cloth, 

 and will be caught by the wire screen, and a strong light will come up through the egg so 

 that the blastoderm can be seen directly. It must be remembered that the 100 watt bulb 

 gives off a great deal of heat so that the examination should not be extended for long. 

 A dark room for the candling is best. 



The blastoderm can be seen by hS hours and the yolk-sac circulation by 60-72 hours. 

 Thereafter, movements of the embryo and the interlacing extra-embryonic circulation be- 

 come increasingly apparent. Embryos which die early generally show coagulation of blood 

 in the sinus termlnalia (blood ring). Prom the seventh to the thirteenth days the chorio- 

 allantoic circulation can be seen, but after the thirteenth day the embryos appear more 

 and more opaque, accentuating the air space at the blunt end. Embryos which die during 

 the latter half of Incubation show an indistinct air space demarcation. 



There are two peaks in the mortality curve of Incubated hen's eggs, one about the 

 third or fourth day and the other Just before hatching, when the extra- embryonic membranes 

 are drying up. Under the most ideal conditions even the best eggs show 5^ mortality on 

 the fourth day, 15^ on the 19th day, and Tf> mortality during the balance of the incubation 

 period of twenty-one days (Romanoff, 1951)' 



TECHNICAL AND OPERATING EQUIPMENT REQUIRED 



Provided by the Institution : 



Temperature-controlled incubator(3) with turning and hatching trays. 



Autoclave 



Dry sterilizing oven 



Heating plates or electrically- controlled stage warmers for warming eggs or 

 embryos during operations. 



Candling equipment 



100 cc. beakers with (soft) paraffin and small (paint-type) brushes 



Absorbent cotton 



Covered containers for discarded eggs 



Spencer microscope lamp, condenser and diaphragm. 



Dissecting microscope 



Round bottom (250 cc.) flask of water supported by double pinch-clamp, to ab- 

 sorb heat from light source. 



Solutions: 



Glass distilled water 



Locke's (1907 Jour. Physiol. 56:208) solution 



NaCl - 0.9 gr. NaHCOj - 0.02 gr. 



KCl - O.OU gr. Diet, water - 100 cc. 



CaCU - O.O2U gr. (anhydrous) (Use at 58° - i+0°C.) 



Physiological saline (0.9^ NaCl) 

 Phenol red (of known concentration) 



MS 222, made up l/5,000 in Locke's of physiological saline (anesthetic). 

 Fixatives: Bouin, Klinenberg's Pi cro- sulphuric, Aceto-formalln. 



