36 MANUAL OF HISTOLOGY. 



especially if great amplification is aimed at. Lenses of very 

 high power are also apt in any case to exhibit the same ap- 

 pearances. 



Measurements of the red corpuscles in man and ani- 

 mals. The average diameter of the human red globule is still 

 a matter of discussion. The faulty measurements of the older 

 writers have led to some misconception on these points, and the 

 matter has required new study. Welcker, who has long been 

 an authority on the Continent, gave .00774 mm. as the average 

 breadth in the human male, with a minimum of .0045 mm., the 

 latter from personal observation. A maximum of .010 mm. 

 has been given by Max Schultze, while Frey places the average 

 thickness at .0018 mm. Later investigations by Hayem show 

 that a diameter of .012 mm. or even .014 mm. may be reached, 

 while he has known it to fall as low as .0022 mm. Elsberg 

 gives the mean diameter of the red blood-corpuscle at .0075 

 mm., agreeing very nearly with Welcker. He has observed a 

 maximum of .01016 mm., and a minimum of .00422 mm. 



Measurements of single corpuscles have no value in deter- 

 mining the particular animal from which the blood has been 

 obtained, and this is an object of prime importance in medico- . 

 legal cases. It is common, therefore, to make a hundred or 

 more single measurements, and then take the average of them. 

 And yet this figure may vary considerably in different individ- 

 uals, or even in the same one. In the blood of the puppy, for 

 instance (the size of the dog's corpuscle being very nearly 

 that of man's), a recent observer found that the average diame- 

 ter of fifty corpuscles varied only two-millionth of an inch 

 from a like average of fifty taken from his own blood. In 

 another instance, taking forty from a puppy, Jie found that 

 the average differed only seven-millionth of an inch from a 

 similar average of his own (Woodward). 



Opposite is given a table of blood-corpuscle measurements 

 by Welcker and others. 



By referring to it, the cat's and rabbit's corpuscles will be 

 found to have an average diameter which is not far distant 

 from man's and dog's, while the minimum and maximum 

 diameters of each show conclusively that a large number of 

 their corpuscles would be likely to equal man's, and there- 

 fore make it impossible to distinguish one from the other. To 

 obviate this source of error a very large number of corpuscles 



