VARIATIONS IN THE COMPOSITION OF HEALTHY BLOOD 143 



crystallized hematin. Although difficult to obtain in bulk, a specimen may 

 be easily made for the microscope in the following way: A small drop of 

 dried blood is finely powdered with a few crystals of common salt on a glass 

 slide and spread out; a cover- glass is then placed upon it, and glacial acetic 

 acid added by means of a capillary pipet. The blood at once turns a brown- 

 ish color. The slide is then heated, and the acid mixture evaporated to 

 dryness at a high temperature. The excess of salt is washed away with 

 water from the dried residue, and the specimen may then be dried and 

 mounted. A large number of small, dark, reddish-black crystals of a rhom- 

 bic shape, sometimes arranged in bundles, will be seen if the slide be sub- 

 jected to microscopic examination, figure i23a. 



The formation of these hemin crystals is of great interest and importance 

 from a medico-legal point of view, as it constitutes the most certain and 

 delicate test we have for the presence of blood (not of necessity the blood 

 of man) in a stain on clothes, etc. It exceeds in delicacy even the spectro- 

 scopic test. Compounds similar in composition to hemin, but containing 

 hydrobromic or hydriodic acid, instead of hydrochloric, may be also readily 

 obtained. 



Scheme to Show the Relations of Hemoglobin .and its Derivatives. 



Variations in the Composition of Healthy Blood. The conditions 

 which appear most to influence the composition of the blood in health are 

 these: Diet, Exercise, Sex, Pregnancy, and Age. 



Sex. The blood of men differs from that of women, chiefly in being of 

 somewhat higher specific gravity, from its containing a relatively larger 

 quantity of red corpuscles. 



Pregnancy. The blood of pregnant women has rather lower than the 

 average specific gravity. The quantity of the colorless corpuscles is in- 

 creased in the later months, especially in primiparse; it is also claimed that 

 the fibrin is increased in amount. 



Age. The blood of the fetus is very rich in solid matter, and especially 

 in colored corpuscles; and this condition, gradually diminishing, continues 



