THE BLOOD. 229 



one direction or the other in certain pathologic states, it is deemed desirable 

 for clinical purposes to determine the extent of this variation. Among the 

 methods suggested for this purpose that of Hammerschlag is the one most 

 generally resorted to. It is based on the principle, that a fluid in which a 

 drop of blood neither rises nor falls must have the same specific gravity as 

 the blood itself. As the specific gravity of the blood varies in different 

 pathologic states it is essential that the fluid employed is of such a character 

 that its specific gravity can be quickly varied in one direction or the other. 

 To meet this indication a fluid, a mixture of chloroform (specific gravity 

 1.526) and benzol (specific gravity 0.889) i s nrst prepared in such propor- 

 tions that the mixture has a specific gravity of about 1.040. With a pipette 

 a drop of blood is then placed in the mixture. If the drop rises the specific 

 gravity of the mixture is greater than that of the blood. Benzol is then 

 gradually added until the drop remains stationary. At this moment the 

 specific gravity of the mixture is the same as that of the blood. If the 

 drop falls the specific gravity of the mixture is less than that of the blood. 

 Chloroform is then gradually added until the drop remains stationary. 

 At this moment the specific gravity of the mixture is the same as that of 

 the blood. In either case the specific gravity of the mixture is determined 

 with a suitable hydrometer and the figure observed attributed to the blood. 



5. Reaction. The reaction of the blood has usually been stated as 

 alkaline from its effect on litmus paper. Thus, if blood is permitted to 

 remain for a few seconds on slightly reddened glazed litmus paper and then 

 washed off, a distinct blue color presents itself against a red or violet back- 

 ground. The alkalinity thus indicated has been attributed to disodium 

 phosphate, Na 2 HPO 4 , and sodium carbonate, Na 2 CO 3 . The degree of the 

 alkalinity is measured by the amount of a standard acid necessary to be 

 added before the indicator used shows an acid reaction. According to 

 v. Jaksch the alkalinity corresponds to from 260 to 300 milligrams of sodium 

 hydrate, NaOH, for every 100 c.c. of blood, according to Lowy from 300 to 

 325 milligrams. The hitherto unavoidable error in these estimates is about 

 30 milligrams. The alkalinity from this point of view varies but within 

 narrow limits in physiologic conditions. It is increased in the early stages 

 of digestion and decreased in the later stages as well as after prolonged 

 exercise. 



In accordance with the ideas of physical chemistry the acidity of a fluid 

 is dependent on the presence of hydrogen ions, H + , and the alkalinity on the 

 presence of hydroxyl ions, (OH). The reaction of any fluid, containing a 

 number of chemic compounds in solution, will be dependent therefore on the 

 relative proportions of hydrogen ions and hydroxyl ions that make their 

 appearance. 



If the hydrogen ions are in excess the fluid is acid, if the hydroxyl ions 

 are in excess the fluid is alkaline in reaction. Tested by the methods of 

 physical chemistry blood and lymph are found to possess these opposite 

 ions in equal degree and therefore are neither acid nor alkaline but neutral 

 in reaction. 



6. Temperature. The temperature varies from 36.78 C. (98.2 F.) in 

 the superior vena cava to 39.7 C. (103.4 F.) in the hepatic vein, the mean 

 being about 38 C. (100 F.). 



