38 THE VITAL PROCESSES 



same manner, and after another half hour add blood to the third. The 

 water dilutes the salts so that coagulation is no longer prevented. Jar 

 the vessel occasionally as coagulation proceeds ; and if the clot is slow 

 in forming, add a trace of some salt of calcium (calcium chloride). After 

 the blood has been added to the last tumbler make a comparative study 

 of all. Note that coagulation begins in all parts of the liquid at the 

 same time and that, as the process goes on, the clot shrinks and is 

 drawn toward the center. 



4. Place a clot from one of the tumblers in experiment 3 in a large 

 vessel of water. Thoroughly wash, adding fresh water, until a white, 

 stringy solid remains. This substance is fibrin. 



5. Examine the coagulated blood obtained from the butcher (bottle 

 2). Observe the dark central mass (the clot) surrounded by a clear 

 liquid (the serum). Sketch the vessel and its contents, showing and 

 naming the parts into which the blood separates by coagulation. 



To examine the Red Corpuscles. Blood for this purpose is easily 

 obtained from the finger. With a handkerchief, wrap one of the fingers 

 of the left hand from the knuckle down to the first joint. Bend this 

 joint and give it a sharp prick with the point of a sterilized needle just 

 above the root of the nail. Pressure applied to the under side of the 

 finger will force plenty of blood through a very small opening. (To 

 prevent any possibility of blood poisoning the needle should be steril- 

 ized. This may be done by dipping it in alcohol or by holding it for an 

 instant in a hot flame. It is well also to wash the finger with soap and 

 water, or with alcohol, before the operation.) Place a small drop of the 

 blood in the middle of a glass slide, protect the same with a cover glass, 

 and examine with a compound microscope. At least two specimens 

 should be examined, one of which should be diluted with a little saliva 

 or a physiological salt solution. 1 In the diluted specimen the red cor- 

 puscles appear as amber-colored, circular, disk-shaped bodies. In the 

 undiluted specimen they show a decided tendency to arrange them- 

 selves in rows, resembling rows of coins. (Singly, the corpuscles do 

 not appear red when highly magnified.) 



A few white corpuscles may generally be found among the red ones 

 in the undiluted specimen. These become separated by the formation 



1 A physiological salt solution is prepared by dissolving .6 of a gram of common 

 salt in too cc. of distilled water or pure cistern water. This solution, having the 

 same density as the plasma of the blood, does not act injuriously upon the 

 corpuscles. 



