682 



HUMAN ANATOMY. 





Sm 



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r 



Red cells from human blood ; 

 tiear centre of field. 



leucocyte seen 



.< 865. 



Dresbach ^ has recorded the presence of elliptical red cells in the blood of an apparently 

 healthy mulatto. The oval corpuscles, which measured .010 mm. by .004 mm., were approxi- 

 mately constant in size, slightly biconcave, and constituted ninety per cent, of all the red cells. 

 They were observed over a period of four months, during which time the number of erythro- 

 cytes and leucocytes and the amount of 

 Fig. 645. hemoglobin were normal. Dresbach con- 



cludes that the oval form was not an arti- 

 fact, but probably due to developmental 

 variation. 



The average diameter of the red 

 blood-cells of man is .0078 mm. 

 (-3 2^0" "^O- some corpuscles meas- 

 uring as little as .0045 mm. and 

 others as much as .0095 mm. Their 

 average thickness is about .0018 mm. 

 "i It is probable that the average diam- 

 ' eter is uninfluenced by sex and is 

 constant for all races, although ac- 

 cording to Gram, the size of the cor- 

 puscles is somewhat greater in the 

 inhabitants of northern countries. 

 The number of red cells normally 

 contained in one cubic millimeter of 

 blood is approximately 5,000,000 in 

 the male and something less (4,500,- 

 000) in the female. The number of 

 corpuscles is practically the same 

 whether the blood be taken from the arteries, capillaries, or veins, but is lower in the 

 blood from the vessels of the lower extremity than of the upper, probably "owing to 

 the greater proportion of plasma in the more dependent parts of the body. Within 

 the first day after birth, the number of erythrocytes is normally very high; in ad- 

 vanced old age it is usually diminished. 



In general, the red blood-cells of mammals are small and their size, which greatly varies in 

 different orders, bears no relation to that of the animal. The corpuscles of man, which are among 

 the largest and exceeded by only those of the elephant (.0094 mm.) and the two-toed sloth 

 (.0091 mm.), are approximated by those of the 



guinea-pig (.0075 mm.), dog (.0073 mm.), rab- Fig. 646. 



bit (.0069 mm.), and cat (.0065 mm.). Those 

 of many familiar mammals are distinctly 

 smaller, as the hog (.006 mm.), horse (.0056 

 mm.), sheep (.005 mm.) and goat (.004 mm. ). 

 The smallest mammalian corpuscles are those 

 of the musk-deer, with a diameter of .0025 mm. 



It is obvious that a positive differentiation 

 of human blood from that of some of the do- 

 mestic animals, based on the measurement of 

 the red cells, is uncertain and often impossible. 

 The application of the "biological" test has 

 placed a much more reliable and even specific 

 means in the hands of the medico-legal expert. 

 This test depends upon the fact, demonstrated 

 by Bordet, Uhlenmuth, and others, that the 

 blood-serum of an animal that has been repeat- 

 edly injected with small quantities of human 

 blood will produce a distinct cloudy precipitate 

 or turbidity when added to a dilute solution 

 of human blood, but will yield no result when 

 added to similar solutions of blood from other animals. An important advantage of this test 

 is that even when the blood is putrid, contaminated, or derived from old dried clots, the char- 

 acteristic changes occur. Certain exceptional disturbing conditions, such as the presence of 



' Science, March 18, '904. and March 24, 1905. 



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■r^ 



J 



Human blood corpuscles ; two leucocytes are 

 seen among the red cells, most of which are 

 grouped in rouleaus. X 625. 



