QUANTITY AND COMPOSITION OF THE BLOOD IN MAN 901 



can be directly read off. It is often possible by working quickly to receive blood into 

 such graduated capillary tubes and to centrifuge it rapidly before it has had time 

 to coagulate. The corpuscles are hurried down to the bottom of the tube within 

 two or three minutes and their volume can be in this way directly determined. 

 An indirect method for the same purpose was devised by Hoppe-Seyler. The total 

 proteins of defibrinated blood are determined and compared with the total proteins 

 of the washed corpuscles and of the serum. Thus in one experiment 100 grm. of 

 defibrinated pig's blood contained 18-90 grm. protein plus haemoglobin. The blood 

 corpuscles of 100 grm. of the same blood contained 15-07 grm. proteins plus haemo- 

 globin; therefore the serum of the same 100 grm. of blood contained 18-90 15-07 = 

 3-83 grm. proteins. One hundred grammes of serum contained 6-77 grm. protein. From 

 these figures the amount of serum in the 100 grm. of defibrinated blood may be 

 computed as follows : 



Q.QQ 



. 100 = 56-6 per cent, serum. 

 6-77 



100 56-6 = 43-4 per cent, blood corpuscles. 



The average volume of corpuscles in human blood can be taken as 50 per 

 (tent, of the total amount, different estimations having given figures varying 

 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 milli- 

 metre 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 cir- 

 culation 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 considerably 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-hsemoglobin, 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 haemo- 

 obin we may measure directly the oxygen capacity of the blood, since 



m 



* 



