98 THE AMERICAN MONTHLY [Apr., 



ism, living a peculiar life, would not only necessarily ap- 

 propriate the chemical constituents suitable to that life, 

 but must appropriate them in a different proportion from 

 any other animal. Unfortunately, the discoveries in this 

 direction, though showing much to support this view, 

 have not yet reached that degree of certainty, which 

 make them reliable indications; whether this can be done, 

 is and important question for the future to settle. In 

 my own experience I have thought that the color of the 

 human blood corpuscles was so different from those of 

 the dog, as to afford a valuable means of discrimination 

 between the two, but I am not prepared to say, that it 

 can always be relied on. This also would depend on first 

 the amount of hemoglobin present and second on the den- 

 sity or specific gravity of the blood corpuscle itself. 



There are four tests for the presence of blood, but only 

 one for the differentiation between human blood and that 

 of other animals, namely, that of the measurement of the 

 blood corpuscles. Of the chemical tests by guiacum and 

 the formation of hematin crystals, it is not the place here 

 to speak, partly because they belong to the domain of 

 chemistry, partly because they only go to the length of 

 declaring that a fluid is blood of some animal. The spec- 

 troscopic test has the same defect, though as the micro- 

 scope is frequently employed, it properly comes within 

 the range of subjects to come before a microscopical so- 

 ciety. This means of identifying blood is entirely con- 

 clusive for the spectra of meth-hemoglobin, hemoglobin, 

 oxyhemoglobin and reduced hematin ; cannot be con- 

 founded by a practiced observer with the spectra of any 

 other substances. 



Now as to the measurement of the blood corpuscles, 

 which is of course, entirely a microscopical matter. The 

 corpuscles, are as is well known exceedingly minute, flat- 

 tened, circular, bi-concave bodies. So numerous that 

 there are from 4,000,000 to 5,000,000 iu a cubic millime- 



