138 SPECIAL PHYSIOLOGY 



necessitate the repetition of the test. Before starting each test see 

 that the pads are in place. 



If the tube is not adjusted in the apparatus and set to rotating 

 within a few seconds after the blood is drawn, coagulation will set 

 in and hinder the complete separation of the corpuscles from the 

 plasma. Should separation not be complete in three minutes the 

 test should be repeated. The instrument should be started and 

 stopped gradually, as the sudden starting and stopping injures it. 



Questions. 1. Determine the volume percentage of red blood 

 corpuscles in a number of normal individuals. 



2. Do apparently normal individuals have the same or approx- 

 imately the same volume percentage of red blood corpuscles ? If not, 

 seek for causes of the variations in different individuals. 



3. Does the same individual have the same volume percentage of 

 red blood corpuscles all the while? 



(a) If there is a variation, is there any periodicity to be observed? 

 (6) Seek for causes of any variation in the same apparently normal 

 individual. 



4. The volume percentage as recorded by the hsematocrit varies with 

 the product of two factors: the average volume of the individual 

 corpuscles by the number of corpuscles per unit volume. (V=vXn). 



(a) Is the average volume of the individual corpuscles (v) neces- 

 sarily constant? 



(6) If it is not constant, would one be justified in drawing con- 

 clusions regarding the number of corpuscle per unit volume (n) after 

 observing the volume percentage (V) with the hsematocrit? 



5. What variation of the observation as above made would enable 

 one to determine with reasonable accuracy the number of corpuscles 

 per cubic millimetre? 



6. If the tube were only partly filled at first, could one make an 

 accurate test? If so, tell how to proceed. 



II. THE ESTIMATION OF THE PERCENTAGE OF COLORING 

 MATTER IN THE BLOOD. 



The estimation of the coloring matter in the blood is based on the 

 supposed fact that a normal individual under normal surroundings has 

 a normal amount of coloring matter, and that is called 100 per cent. 



The instruments that have been devised for making the estimation 

 are numerous, and all, while theoretically correct, practically are 

 liable to a greater or less error according to the experience and 

 carefulness of the observer. They are, however, in a skilful and 

 conscientious operator's hands, quite accurate, and are especially 

 so when used to compare the tests of the same patient's blood, week 

 by week. 



