ANIMAL FLUIDS AND TISSUES. 651 



matter, it is necessary to determine them either in the aqueous solution 

 (extract) or by subjecting the animal matter to dialysis, by which process 

 they may be more or less completely separated from the organic matter, 

 which is left in the dialyzer, while the salts pass through the membrane. 



Blood. Two kinds of blood are distinguished, the arterial or oxi- 

 dized and the venous or deoxidized blood. Arterial blood as it is 

 present in the system, or immediately after it has been drawn from 

 the body, is a red liquid of an alkaline reaction and a specific gravity 

 of about 1.055. Upon examination under the microscope blood is 

 seen to consist of a colorless fluid, called plasma, in which float small 

 globules or corpuscles, which make up about 40 per cent, of the whole 

 volume of blood. These corpuscles are of three varieties, viz., red 

 and white corpuscles, and blood-plates. The red corpuscles of blood, 

 or erytkrocytes, which give to the blood its color, are biconcave, cir- 

 cular, non-nucleated disks, about ^W of an inch in diameter. When 

 viewed through the microscope they are of a faint greenish-yellow 

 color, while en masse they show the color of arterial blood. The 

 white corpuscles of blood, or leucocytes, are round or irregularly shaped 

 nucleated cells ; they are devoid of coloring-matter, and are far less 

 numerous than the red corpuscles. The blood-plates are colorless, 

 oval, round, or lenticular disks, measuring generally less than one- 

 half of the diameter of red corpuscles. 



Specific gravity. This varies in healthy adults between 1.046 and 

 1.067, but under pathological conditions may vary between 1.025 

 and 1.068. 



The specific gravity can be determined by permitting a drop of blood to fall 

 into a mixture of chloroform and benzol presenting a specific gravity of about 

 1.055. If the drop sinks to the bottom, more chloroform must be added ; if it 

 floats on the surface, benzol has to be added until it floats midway in the 

 liquid. The specific gravity of the mixture, which is now identical with that 

 of the blood, is determined by a delicate hydrometer. 



Reaction. The alkaline reaction of blood is due to the presence 

 of sodium bicarbonate, NaHCO 3 , and disodium phosphate, Na 2 HPO 4 , 

 both of which have a weak alkaline reaction. "While blood reacts 

 alkaline to litmus, it is neutral to phenol phthalein, and according to 

 the newer concept of alkalinity (an excess of dissociated hydroxyl 

 ions over the dissociated hydrogen ions present) it is nearly neutral. 

 For clinical purposes it is still regarded as alkaline, and the extent 

 of this alkalinity to litmus or lacmoid has some importance. There 

 are no very satisfactory methods of titration. That one most used 

 (Dare) depends upon the disappearance of the spectrum of hsemo- 



