578 Anatomy, Physiology, and Pathology of the 



fibrine exist in every 1000 of blood ; but it becomes increased in 

 inflammatory affections, and often rises to 8 or 10 parts in the 

 same quantity. This fact explains why a larg^er amount of blood 

 can be abstracted during the acute stage of inflammation than in 

 health, without the system suffering to an equal extent. 



We pass on to ponsider the serum. After the coagulum of 

 blood has stood at rest for a short time, a fluid of a pale straw- 

 colour appears on its surface : this is the serum. The separation 

 of the serum from the clot is due to the contraction of the fibrine, 

 which continues long after the blood has coagulated. The fluid 

 therefore is forcibly expelled ; being, prior to its separation, me- 

 chanically retained in the coagulum, as water may be said to be 

 in a sponge. Serum holds in solution the albumen and salts of 

 the blood, and it is chiefly composed of these matters with the 

 addition of water. Its viscosity will depend on the relative amount 

 of albumen, which in health has been estimated at about 8 per 

 cent. An alteration in the specific gravity of serum will likewise 

 indicate the proportion of its albumen; as in healthy subjects its 

 specific gravity is about 1030. Under disease, and more espe- 

 cially when of a debilitating nature, such as dropsy, the watery 

 parts of the serum are increased, and become effused into various 

 cavities of the body, as the chest, abdomen, or ventricles of the 

 brain. Ordinary serum is also quickly transuded through the thin 

 coats of the capillary vessels, of which we have daily proofs in 

 local inflammation of the external structures, where the swelling 

 is referable to that cause. Unlike fibrine, serum, whether in or 

 out of the body, remains fluid ; but as it contains albumen, this is 

 capable of being solidified by heat, and likewise by the admixture 

 of mineral acids, or alcohol.* The heat required to accomplish 

 this is 162° of Fahrenheit — a temperature the body never attains 

 to. Albumen is believed to be converted into fibrine, and thus 

 to minister to nutrition ; and it is also thought that the white cor- 

 puscules of the blood, of which the limits of this lecture will not 

 allow of a further mention, are the agents which effect the con- 

 version. The salts can be only incidentally alluded to ; they 

 amount to between 6 and 7 parts in 1000, and are chiefly com- 

 posed of the chlorides of sodium and potassium, and the phos- 

 phates of lime, magnesia, and soda. 



Having now described the constituents of the blood, we pass 

 on to explain its circulation, and the changes which take place 

 during its passage from one part of the system to another. We 

 have before likened the heart to a central pump, as it is by the 

 contraction of the muscular walls of this organ that the blood is 



* The solidification of the albumen of serum was demonstrated in the lecture by the 

 employment of hydrochloric acid. 



