QUANTITY AND COMPOSITION OF BLOOD 857 



determination of the relative carbonic oxide saturation of the blood 

 sample. 



The total blood volume probably varies appreciably with alterations 

 in the conditions of the animal, and may be found different on two suc- 

 ceeding days. It is certainly influenced by the height of the blood pressure 

 as well as by the oxygen tension in the air breathed, and therefore alters 

 with the altitude. Some of these variations we shall have to consider more 

 fully in a later section. Any lowering of blood pressure causes an absorp- 

 tion of fluid from the tissues into the blood, so that the latter becomes more 

 dilute. The blood content during the last stages of bleeding may contain 

 little more than 50 or 60 per cent, of the haemoglobin which was present 

 in the first samples of blood, pointing to a corresponding dilution of the 

 blood during these few minutes by means of tissue lymph. By this means, 

 i.e. the absorption of fluid from tissues, the volume of circulating blood 

 after a limited haemorrhage is rapidly brought up to normal, so that there 

 is a circulation of a fluid impoverished in corpuscles. The latter are made 

 up in the course of a few weeks as a result of increased activity in the 

 bone-marrow. 



RELATIVE AMOUNT OF PLASMA AND CORPUSCLES 



The relative amount of corpuscles in a given sample of blood is most 

 easily determined by Blix's method. The blood is mixed with a definite 

 amount of 2*5 per cent, potassium bichromate, and the mixture is put 

 into small graduated capillary tubes, which are then placed in a centrifuge 

 revolving about 10,000 times per minute. The corpuscles rapidly accumu- 

 late in an almost solid mass at the bottom of the tube, and their volume 

 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 de- 

 fibrinated pigs' blood contained 18-90 grm. protein plus haemoglobin. The 

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

 proteins plus haemoglobin ; therefore the serum of the same 100 grm. of 

 blood contained 18-90 ~ 15 -07 = 3-83 grm. proteins. One hundred grammes 

 of serum contain 6-77 grm. protein. From these figures the amount of 

 serum in the 100 grm. of defibrinated blood may be computed as follows : 



3-83 



r^ry.100 = 56-6 per cent, serum. 



10056-6 = 43-4 per cent, blood corpuscles. 



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

 cent, of the total amount, different estimations having given figures varying 



