144 SPECIAL PHYSIOLOGY 



the blood and water by shaking or rolling the tube gently. Do noi 

 place the thumb over the end and shake, as an appreciable amount 

 of color will be lost and a foam is formed that delays the reading. 



Now place the tube in the rubber block beside the tube containing 

 the standard solution and add distilled water, drop by drop, to the 

 diluted blood, always shaking the tube between the additions tc 

 keep the blood and water well mixed. Continue this until the color 

 of the blood solution is not darker nor lighter than the standard 

 solution. The comparison of the colors is made either by trans- 

 mitted or reflected daylight. The eye will be assisted by placing 

 the tube behind a piece of white paper and holding them toward 

 the window light. The reading is made directly from the graduated 

 tube, in percentage of haemoglobin when the color of the diluted 

 blood is the same as the standard solution. Repeat the test until 

 the same result is obtained continually. 



Precautions. If air bubbles are drawn up into the capillary, or 

 if it is either over or underfilled, the tube must be recleaned and 

 dried and the test repeated until done accurately. If the pipette 

 contains moisture or foreign matter the measurement will not be 

 accurate. Always remove any blood that may happen to get on the 

 outside of the pipette, as it will increase the result. It is a good plan 

 to have a large drop of blood ready before you begin to fill the pipette, 

 rather than to take two or three small drops. Because of the time 

 consumed to obtain the amount of blood needed there is liability 

 of the blood clotting and sticking in the capillary. When only 

 partially clotted the blood is blown into the graduated tube and 

 remains as a clotted thread in the bottom. Gently striking the finger 

 against the tube or shaking the tube sidewise is sufficient to mix 

 the blood and water, and is far better than placing the thumb over 

 the mouth of the tube and shaking it up and down. If this latter 

 method is used it will make a difference of 5 to 10 per cent, in results. 

 Always be sure to wash the capillary out a number of times and 

 place the washings in the graduated tube, or the result obtained will 

 be less than the test should show. If a tube has been partially or 

 improperly filled, do not leave it so; always blow out the blood before 

 it can clot, and much time will be saved. A reading should be 

 made each time and recorded before more water is added, for if 

 one should dilute the blood too much and had no record of the last 

 reading the test is spoiled and the work lost. 



C. Dare's Hsemoglobinometer. 



Appliances. Dare's haemoglobinometer, a candle, and a glover's 

 needle, 



Preparation. Dare's instrument estimates the percentage of 

 haemoglobin by comparing the color of a thin film of blood of a cer- 



