CRYSTALS OF HEMOGLOBINS EMPLOYED IN THIS RESEARCH. 147 



through, the formation of successive crops of oxyhemoglobin and also 

 reduced hemoglobin, methemoglobin, and metoxyhemoglobin were observed. 

 Some crystals kept well for weeks, some altered inside of a day or two. In 

 general the best results were obtained with crystals that formed at room 

 temperature and did not dissolve on slight increase of temperature, but 

 in many cases all the observations had to be made near freezing tem- 

 peratures. This was done by working in a cold room, at a temperature 

 near C. Even at such a temperature the heat of the body or breath often 

 produced partial solution of some of the crystals, so that the measurements 

 had to be made rapidly. Having usually a number of slides at hand, this 

 could generally be done conveniently, as, when the crystals began to lose 

 shape, the slide under investigation could be replaced by another from the 

 supply kept at a temperature below freezing, and the crystals of the first 

 slide would usually soon regain their form. When the blood crystals were 

 not very soluble it was always found more advantageous to keep them at a 

 temperature much above freezing rather than near the freezing-point; they 

 could then be examined and photographed without fear of solution because 

 of an increase of temperature. 



