VI.] 



THE COLOURED BLOOD CORPUSCLES. 



45 



(e ) Wash the instrument, and in cleaning the cell do this with 

 a stream of distilled water from a wash-bottle. Take care not to 

 brush the cell with anything rougher than a camel 's-hair pencil to 

 avoid injuring the lines. 



Each square has an area of ^ of a square mm., so that 10 

 squares have an area of T V of a square mm. As the cell is I mm 

 deep, the volume of blood in 10 squares is T ^ x i = J^ c.mm'. On 

 counting the number of corpuscles in 10 squares, and multiplying 

 by 50, this will give the number in i c.mm.. of the dilut&l blood" 

 On multiplying this by 10^0, W e get the number in i c.mm. before 

 dilution. Thus we arrive at the reason why we multiply the 

 number in 10 squares by 10,000 to get the number of corpuscles in 

 i c.mm. of blood. 



HEMOGLOBIN AND ITS DERIVATIVES. 



3. Preparation of Haemoglobin Crystals, (C ( , 00 H 960 N 154 179 SFe). 



(a.) Rat's Blood. Place a drop of defibrinated rat's blood on a 

 slide, add three or four drops of water, 

 mix. and cover with a cover-glass. Ex- 

 amine with a microscope ; after a few 

 minutes small crystals of oxy-haemo- 

 globin will begin to form, especially 

 at the edges of the preparation, and 

 gradually grow larger in the form of 

 thin rhombic plates arranged singly or 

 in groups (tig. 21). 



(b.) Guinea-Pig's Blood. Treat the 

 blood of a guinea-pig as directed for 

 the blood of a rat. Tetrahedral crystals 

 are obtained. Mount some defibrinated 

 blood in Canada balsam. Crystals 

 form. 



FIG. si. Haemoglobin Crystals 



(c.) Dog's Blood. To 1500. of defibrinated from Bat's Blood, 



dog's blood add, drop by drop, i cc. or 



so of ether, shaking the tube after each addition of ether. By this means 

 the blood is rendered laky, a condition which is recognised by inclining 

 the tube, and observing that the film of blood left on it, on bringing the 

 tube to the vertical again, is transparent. Add no move ether, but place the 

 tube in a freezing mixture of ice and salt ; as the temperature falls, crystals 

 of haemoglobin separate. If the crystals do not separate at once, keep the 

 tube in the freezing mixture for one or two days. Examine the crystals 

 microscopically. Arthus finds that dog's blood, containing I per cent, of 

 sodic fluoride, after standing for several days, according to the surrounding 

 temperature, deposits crystals of lib. 



