74 The Microscope. 



red larvoe of the feather-fly, Chironomus plumosous. These flies 

 are not parasites ; they suck no blood. This proves that the red 

 coloring pigment which forms in their bodies, orii^inates from purely 

 vegetable substances. Chlorophyl gives an absorption band in the 

 neighborhood of sulphurated hydrogen spectrum. We may at 

 times give a negative answer. The microscope can tell us where the 

 size and form of the corpuscles differ from those of man, and 

 whether such blood belongs to inferior animals — for example, the 

 frog's blood. It can also, by the peculiar form of crystallization, 

 tell us what it is not. We know that human blood and that of 

 many carnivorous animals, crystallizes in prisms. The blood of the 

 guinea-pig, of the rat, the mouse and other rodents crystallizes in 

 tetrahedrons. The blood of the squirrel forms hexagonal tablets ; 

 hamster -blood crystallizes in rhombohedra, and fish blood in fine 

 prismatic needles. The blood of various animals differs, also, in 

 solubility. ' 



Human blood solves very readily ; the blood of monkeys, 

 hedge-hogs, and others, solves equally easily. The blood of the 

 guinea-pig, the squirrel, the rat and other rodents, on the contrary, 

 solves with great difficulty. There is also great difference in the 

 sinking capacity of the corpuscles. Horse blood, for example, 

 possesses the greatest sinking power, forming rapidly a layer of 

 blood corpuscles in the serum when collected in a glass vessel. Some 

 blood will crystallize rapidly ; another with far greater difficulty. 

 These facts may assist to answer the inquiry as to the identity of 

 human blood. 



I have purposely given a more ample description of this blood 

 crystallization, the only crystallizable albumen known, because upon 

 this important knowledge will rest the possibility to understand 

 what follows. 



OPTIC RELATIONS OF BLOOD AND ITS CRYSTALS. 



'When undiluted blood is spectroscopically examined, we 

 observe a dark spectral field, relieved only by a nebulous band in 

 the red part of the spectrum near A. Examine carefully this 

 spectral appearance on the spectroscopic diagram No. 3. The 

 wood-cutter made this line too thick. If we dilute the solution we 

 observe that light between C and D emerores out of darkness. This 

 evolution of light is rapid. If we continue to dilute until the D 

 line emerges from darkness and becomes visible, using, of course, 

 sunlight, we observe the appearance of green light between the 

 lines B and F. Continued dilution favors the expansion of the 



