The blood was drawn quickly by suction and 

 then immediately expelled from the tube onto the 

 warmed glass slide. As the blood leaves the 

 cannula the tip is moved back and forth so as to 

 distribute the cells and prevent them from piling 

 up in heaps. If there is any delay in entering 

 the aorta, in taking the blood, in making the 

 preparation, or in drying it, the cells will be dis- 

 torted. This is especially likely to happen if 

 contaminating fluids have entered the cannula 

 ahead of the cells or along with them. Efforts 

 to prevent distortion of cells by other means were 

 made. Heparin and silicone coatings over the 

 inside of the cannulas were tried. Neither 

 method gave improvement over careful, rapid 

 use of a clean, dry tube. Essentially the same 

 procedure was used for embryos a day older. 

 The filter-paper 'rings used to hold the embryo 

 were slightly larger than those for 48-hour 

 embryos. 



Method of taking blood from the heart of 

 embryos of 96 hours and older 



The same type of cannula was used as described 

 previously except that it had a slightly larger 

 bore. A cannula with a still larger bore was 

 used when embryo age increased. A different 

 technic was used to procure blood from the sec- 

 ond week of incubation to hatching. 



After S to 6 days of incubation the procedure 

 of moving the tip of the cannula back and forth 

 across the slide, as the blood was being expelled, 

 was discontinued and a new procedure was be- 

 gun — a drop of blood was placed on the end of the 

 smear slide and distributed with a pusher slide. 

 In still older embryos, the tip of the heart was 

 cut open and the drop collected directly onto the 

 end of a pusher slide, but in doing this there must 

 be freedom from fluids around the heart, and 

 the heart should be elevated above the surround- 

 ing tissue. At about mid-embryonic age of in- 

 cubation this drop of blood will often be carried 

 across from one end of the slide to the other and 

 will leave only a few scattered cells over the sur- 

 face of the slide. The ways in which the physical 

 properties of the blood at this age differ from 

 those that obtain just before hatching and after 

 hatching is not known, but obviously the blood 

 has a poor affinity for glass. Schechtman ( 1952 ) 

 showed that the surface tension was less in the 



embryo than in the chick after hatching, and this 

 may be one of the factors that influence the spread 

 of the blood over the glass slide. The difficulty 

 usually can be circumvented by placing the 

 pusher slide at a low angle, by barely touching 

 it against the smear slide, and by giving it one 

 quick movement to the opposite end. 



The infrared lamp and its use in drying 

 and uarming slides 



A tripod carrying an infrared bulb vertically 

 suspended (fig. 412) has been used for many 

 years in this Laboratory in making blood smears. 

 The legs and braces were made from 1/^-inch 

 wires welded together. On top was a flat tri- 

 angle of sheet metal with a hole large enough 

 to receive a light socket. An infrared bulb was 

 placed in the socket. Clean paper toweling or 

 cloth was spread on a table beneath the bulb, and 

 on this the slides were stacked. Usually the 

 slides were stacked around the margin of the cir- 

 cle of light and then about a dozen were spread 

 under the light. 



The heat from the lamp drives the moisture 

 from the slides, and when the smear is made the 

 film of cells dries quickly. It was necessary to 

 have the warmed slides close to the point where 

 they were being used; otherwise, the slide cooled 

 before the film was spread. The pusher slides 

 should not be heated. If the slide is too hot, 

 artifacts will appear. They will be similar to 

 those that appear in erythrocytes (see chapter 

 2 ) . After the smear is made the slides may be 

 retuined to the lamp for complete drying of the 

 cells or they may be put directly into a box. In 

 either case, they are gently heated again just be- 

 fore staining in order to drive off any moisture 

 that may have accumulated when the slides were 

 cooled. 



Method for collecting and carrying blood 

 samples 



Denington and Lucas (1955) have described 

 a box in which 15 units can be carried con- 

 veniently and safely (fig. 413) . The tray hold- 

 ing the red-cell pipettes is removable. Upon re- 

 turning to the laboratory, the worker can separate 

 the tray from the rest of the equipment and place 



227 



