72 PATHOLOGY. 



These several constituents are subject t!> some variations con- 

 sistent with health. Thus the water varies in quantity accord- 

 ing to the period since food has been eaten, the amount of bodily 

 exercise, the state of the atmosphere, and all other events that 

 affect the ingestion or the excretion of fluids. According to 

 these conditions, it may vary from 700 to 800 parts in 1000, 

 On the whole, however, a degree of uniformity is maintained, 

 because nearly all those things which tend to lower the pro- 

 portion of water in the blood, such as active exercise, or the 

 addition of saline and other solid matter, excite thirst ; while, 

 on the other hand, the addition of an excess of water to the 

 blood is quickly followed by its more copious excretion in sweat 

 and urine. 



Dr. Zimmerman has shown that the quantity of water in the 

 Ijlood is increased during its abstraction from an artery or vein. 

 In bleeding dogs he found that the last drawn portion contained 

 12 or 13 parts more of water in 1000 than that first drawn. 

 This experiment goes to prove that the fluid of the tissues must 

 be rapidly absorbed during the operation. 



The water in the economy is required for many important pur- 

 poses, (1.) The proper viscidity of the blood, and the degree of 

 its adhesion to the blood-vessels, is due to the presence of water 

 in proper proportion. (2.) It determines to a great extent the 

 volume of the blood. (3.) Water is the general solvent of the 

 other materials of the liquor sanguinis. (4.) The activity of 

 absorption by the blood-vessels depends upon the due fluidity of 

 the materials to be absorbed, for it is well known that no fluids 

 quickly penetrate the vessels but such as are of lesser densitj^ 

 than the blood. 



If the presence of water in excess continues beyond a short 

 period, it is a certain symptom that the other constituents are 

 defective in quantity, and that the condition termed anaemia is 

 present. 



Deficiency of water in the blood is witnessed in super-purga- 

 tion, diarrhoea, &c. The deficiency, however, is generally of a 

 temporary character, for nature prompts the animal to over- 

 come it by drinking freely. The water also becomes deficient 

 when an animal sweats profusely from any cause, and when 

 prevented from allaying his thirst for a considerable period, as 

 when hunting or going long journeys. A great mistake is made 



