148 SPECIAL PHYSIOLOGY 



straight to the bottom and adhere with the force of the fall. The 

 difficulty with the pipette can be overcome easily by using a pointed 

 glass rod. Secure the drop of blood on the point of the rod and shake 

 it off into the solution. The benzole and chloroform evaporate very 

 rapidly and change the specific gravity of the mixture. The two 

 liquids do not stay mixed, but need stirring frequently. Do not 

 attempt to work with the same drop of blood more than two minutes; 

 take a fresh drop and continue. Make the specific gravity of the 

 mixture as near that of the blood as possible before adding the second 

 drop. One or two drops will always determine approximately what 

 the specific gravity of the blood is; then take a third drop and prove 

 it exactly. The solutions of benzole and chloroform can be put into a 

 glass-stoppered bottle and used again; so there is little waste except 

 from evaporation. This is one of the best tests for obtaining the per- 

 centage of haemoglobin, as the personal equation is largely eliminated 

 and the burden of accuracy is placed upon the instrument. 

 Questions. 1. Why make the mixture 1.060 to begin with? 



2. What is the specific gravity of benzole? Of chloroform? 



3. Why are they better than other solutions for a quick test? 



III. EXAMINATION OF FRESH BLOOD. 



A. Coagulation of Normal Blood. 



The coagulation of normal blood is a phenomenon that takes place 

 quite constantly in from three to five minutes. But in disease this 

 time may be prolonged indefinitely. The coagulation may be approx- 

 imately tested by taking a large drop of blood on a warmed slide, and, 

 while holding it in the hand, draw through the drop a needle or a 

 straw from an ordinary broom every quarter or half-minute, and note 

 when a clot follows the straw out of the drop. Wright's instrument 

 for testing coagulation is slightly more accurate. 



Questions. 1. What is coagulation? 



2. What becomes of the corpuscles? 



3. Is there any variation in the time of coagulation among the 

 individuals in your section? 



B. Microscopic Examination of Blood. 



The microscopic examination of fresh and stained blood is of 

 great clinical importance. In quite a number of diseases it gives a 

 specific diagnosis which could not otherwise be gained. 



Appliances. Microscope, with one-eighth or one-twelfth oil- 

 immersion objective ; eye-piece micrometer ; white ground-glass slides, 

 seven-eighths inch square; No. 1 cover-glasses; glover's needle, and 

 alcohol lamp or Bunsen flame. 



