36 



with a drop of 2% aq. sol. of chloral hydrate, and covered and 

 sealed and allowed to stand for several days, when crystals of oxy- 

 hemoglobin appeared. Note their shape and color. 



55. Hemin. Place upon a slide a little powdered blood (from 

 a dried blood clot or stain), and a few granules of common salt (so- 

 dium chlorid), grinding well together. Add two or three drops of 

 glacial acetic acid and cover. Heat gently two or three times until 

 the acid just boils, adding a fresh drop of the acid after each boiling. 

 Allow it to cool, remove the cover and permit the matter on the 

 slide and cover to dry. Examine both, dry and mount in balsam 

 the one showing best the crystals of hemin. If there are rough 

 lumps of blood in the preparation, they may, without injuring the 

 preparation, be removed by scraping before mounting. A large 

 number of hemin crystals will probably be found. Their shape and 

 color are characteristic and afford one of the best tests of blood. 



THE SPECTRA OP BLOOD. 



56. A demonstration of the spectra of hemoglobin and oxy- 

 hemoglobin will be given. Note the characteristic absorption bands 

 of each and their points of occurrence in the spectrum and the dif- 

 ferences between the spectra of hemoglobin and oxy-hemoglobin. 

 It is advisable to read in some work on physics about the spectro- 

 scope and spectrum analysis ; also microscopical methods, §§ 179- 

 203. 



