384 A Method of Estimating the Total Volume of Blood, etc. 



destruction. In such cases, and also when the degree of haemoglobinaemia was 

 slight, we employed a Zeiss comparison spectroscope, provided with a cell of 

 variable height, the estimation being made by matching the oxyhemoglobin 

 bands of the plasma with those of a solution of haemoglobin of known 

 concentration. 



The accuracy of this method of estimating the total volume of the blood 

 depends upon the precision with which : (1) the haemoglobinometer readings 

 (or the comparison spectroscope determinations) are made ; (2) the condition 

 of the plasma immediately after injection is ascertained. 



In our observations the variation of successive hsemoglobinometer readings 

 of the same solution of haemoglobin did not exceed + 2 per cent, of the mean 

 reading. 



The mode of ascertaining the degree of haeraoglobinaemia immediately after 

 injection is a matter of importance. If only a small percentage of 

 haemoglobin, representing less than 1 per cent, by volume of red cells, is 

 present, no correction is ordinarily required when the plasma is obtained 

 within three minutes of the injection, which generally occupies about one 

 minute. If, however, a sample of blood cannot be obtained so soon after 

 injection, or again if a much higher degree of haemoglobinaemia has been 

 produced, then an amount of dissolved haemoglobin sufficiently large to affect 

 the determination of the blood volume may have disappeared before the 

 sample is obtained. In such cases, two or three determinations of the degree 

 of haemoglobinaemia require to be made at short intervals as soon as possible 

 after injection. From these the percentage of dissolved haemoglobin present 

 in the plasma immediately after injection can be calculated. In a series of 

 observations upon the rate of disappearance of dissolved haemoglobin from 

 the blood plasma in the living body, which will shortly be published,* the 

 mode in which this calculation may be made will appear. 



The advantage of the above method lies in the ease of its application, and 

 the circumstance that the injection of haemoglobin is not attended with any 

 recognisable alteration of the general condition. 



* ' Annals of Tropical Medicine and Parasitology,' 1909, vol. 3, p. 1. 



