BLOOD AND LYMPH 249 



In the application of blood-letting or venesection it has been cus- 

 tomary to discard both the corpuscles and plasma of the withdrawn 

 blood. Abel 1 and associates have found it possible to separate the 

 corpuscles from the removed blood by centrifugation and to return 

 them to the body suspended in Locke's solution. They name the pro- 

 cedure plasmaphceresis . By this means blood-letting can be carried 

 out repeatedly during a short interval of time without endangering the 

 life of the animal. 



There has been considerable controversy regarding the form of the 

 erythrocytes or red blood corpuscles of human blood. It is claimed by 

 some investigators that the cells are bell-shaped or cup-shaped. As the 

 erythrocytes occur normally in the circulation, however, they are prob- 

 ably thin, non-nucleated, biconcave discs. 2 



The blood of most mammals contains erythrocytes similar in form 

 to those of human blood. In the blood of birds, fishes, amphibians and 

 reptiles the erythrocytes are ordinarily more or less elliptical, biconvex 

 and possess a nucleus. The erythrocytes vary in size with the different 

 animals. The average diameter of the erythrocytes of blood from 

 various species is given in the following table: 3 



Elephant y*W of an inch. 



Guinea-pig ^j of an inch. 



Man ^<j of an inch. 



Monkey ^^ of an inch. 



Dog rJri of an inch. 



Rat 3^2 of an inch. 



Rabbit rsW f an inch. 



Mouse -$%-$ of an inch. 



Lion TfW f an inch. 



Ox ^VT of an inch. 



Horse ^sVg- of an inch. 



Pig JjT8 of an inch. 



Cat ^sW f an inch. 



Sheep Wrs of an inch. 



Goat ^tW f an inch. 



Musk-deer 1^3^-5 f an inch. 



The erythrocytes, from whatever source obtained, consist essentially 

 of two parts, the stroma or protoplasmic tissue and its enclosed pigment, 

 hemoglobin. For human blood the number of erythrocytes present in 

 the fluid as obtained from well-developed males in good physical condi- 

 tion is about 5,500,000 per cubic millimeter. 4 The normal content of 

 the blood of adult females is from 4,000,000 to 4,500,000 per cubic 



1 Abel, Rowntree, Turner, Marshall and Lamson (see Abel's Mellon Lecture," 1915): 

 also Abel: Science, 42, 135, 1915. 



2 When examined singly under the microscope, they possess a pale greenish-yellow 

 color (see Plate IV, opposite), whereas when grouped in large masses a reddish tint is 

 noted. 



3 Wormley's Micro- Chemistry of Poisons, second edition, p. 733. 



4 This statement is based upon observations made upon the blood of athletes in training. 

 See Hawk: Amer. Jour. Physiol.,io, 384, 1904. It is generally stated in text-books that 

 the blood of males contains about 5,000,000, per cubic millimeter. 



