THE BLOOD-CORPUSCLES. 155 



children than in adults ; in pregnant women it is even lower than 

 in women who are not pregnant. 



Nasse,* whose labours have contributed very much to our 

 knowledge of the blood, found that its capacity for heat stood in 

 an exact ratio to its density. 



The colour of the blood, as we usually see it, may be described 

 as a bright cherry red; it is clearer in early youth than in the 

 foetal state, in infancy, or in old age ; it is somewhat darker in 

 pregnant than in non-pregnant women. The use of various kinds 

 of food and drink, bodily exercise, and other physiological relations, 

 to a certain degree influence the depth of the blood's colour. The 

 action of gases and other substances on the colour of the blood 

 will be noticed in a future page. 



While still warm, the blood has a peculiar odour, which is 

 generally somewhat stronger in men than in women. 



The blood coagulates, the process commencing in from two to 

 five minutes after its abstraction, at the surface and edges, when it 

 gradually becomes tough and gelatinous ; in the course of from 

 seven to fourteen minutes, the jelly which is thus formed has 

 attained such a consistence that the whole mass has assumed the 

 form of the interior of the vessel, and has lost all its fluidity. 

 The separated substance through which the whole blood has been 

 converted into a jelly, now begins gradually to contract, so that a 

 great part of the fluid inclosed by it is pressed out towards the 

 surface ; this expressed fluid we name serum. The contraction of 

 the gelatinising substance continues for a period varying from 

 twelve to forty hours, during which time a dense red clot or 

 coagulum, the blood-clot, is formed ; this usually assumes the form 

 of the interior of the vessel on a reduced scale ; the lower part 

 of the clot is generally darker, and the upper of a brighter red 

 than the original uncoagulated blood. In men the coagulation 

 proceeds more slowly, but the coagulum is denser, than in women. 

 Arterial blood coagulates more rapidly than venous. Atmospheric 

 air hastens the coagulation ; regarding the influence of temperature 

 on this process, there are still different opinions. By shaking, 

 stirring, or whipping freshly-drawn blood, the coagulating sub- 

 stance separates in yellowish flocculi or pellets, while the fluid 

 remains as red as the uncoagulated blood (or perhaps a little 

 lighter in tint) and equally untransparent. 



Since the times of Malpighi and Leeuwenhoek, it has been 

 known that the blood is not a simple solution of various substances, 

 but an emulsive fluid in which solid particles are contained in suspen- 

 * Handworterbuch der Physiol. Bd. 1, S. 79. 



