858 PHYSIOLOGY 



from 48 to 54 per cent. In the horse the volume of corpuscles is 53 per 

 cent., in the dog 36 per cent. 



THE ENUMERATION OF THE CORPUSCLES 



In order to enumerate the red corpuscles the blood is diluted with a 

 known amount of an isotonic fluid and the number is counted in a measured 

 volume of the mixture. The average number of red corpuscles is about 

 5,000,000 per cubic millimetre in adult men and rather fewer, about 4,500,000 

 in adult women. The enumeration of corpuscles is subject to considerable 

 errors, probably not less than 10 per cent. Moreover different conditions 

 of the circulation may cause variations in the relative distribution of plasma 

 and corpuscles respectively in different parts of the circulation, so that the 

 blood-count of a specimen from the capillaries of the finger or lobe of the 

 ear may vary considerable from a similar count of the corpuscles in blood 

 obtained directly from a minute vein or artery. More important therefore 

 is the determination of the haemoglobin. For this purpose a measured 

 quantity of the blood, 2 to 5 c.mm., is obtained in a capillary pipette and 

 mixed with a given volume of water. The red fluid thus obtained is com- 

 pared with a standard. This latter in von Fleischl's instrument is a prism 

 of coloured glass. In Oliver's instrument the standard consists of a series 

 of tinted glasses, one of which represents the colour of a measured quantity 

 of normal blood diluted with water and placed in a flat glass cell of a certain 

 size, while the others represent percentages of haemoglobin below and above 

 the normal. The most accurate method is that due to Hoppe-Seyler and 

 Haldane, namely, the conversion of the blood sample into CO-haemoglobin 

 and its comparison with a standard specimen of CO-haemoglobin, which is 

 stable in solution and can therefore be kept in a sealed glass vessel for any 

 length of time. 



THE OXYGEN CAPACITY OF THE BLOOD 



Instead of determining the haemoglobin we may measure directly the 

 oxygen capacity of the blood, since the oxygen-binding power of this fluid 

 is entirely dependent on the amount of haemoglobin it contains. For this 

 purpose we may make use of the fact discovered by Haldane, that the 

 combined oxygen in oxyhaemoglobin is liberated rapidly and completely 

 on addition of a solution of potassium ferri- cyanide to laked blood, and 

 may thus be easily measured with the help of an apparatus similar to that 

 used for determining urea in urine by the hypobromite method. 



The following description of the method is given by Haldane : 

 "Twenty cubic centimetres of the oxalated or defibrinated blood, thoroughly 

 saturated with air by swinging it round in a large flask, are measured out from a pipette 

 into the bottle A, which has a capacity of about 120 c.c. As it is important to avoid 

 blowing expired air into the bottle the last drops of blood are expelled from the pipette 

 by closing the top and warming the bulb with the hand." Thirty cubic centimetres 

 are then added of a solution prepared by diluting ordinary strong ammonia solution 

 (sp. gr. 0-88) with distilled water to -g^. The ammonia prevents carbonic acid from 

 coming off, while the distilled water lakes the corpuscles. The blood and ammonia 



