212 SERUM USES OF BLOOD. 



matter of the serum bears to the whole mass of blood, in 

 health, is about 53 parts in 1000 ; and of these about 40 

 parts are albumen, 8 parts saline matter, and 5 parts fat, with 

 certain ill-defined substances, of which some appear to be 

 organic compounds that are undergoing metamorphosis into 

 solid tissues, whilst others are the products of the decay of 

 the tissues, which are being progressively withdrawn and 

 eliminated by the excretory organs. 



239. The influence of the Blood as a whole upon the 

 animal as well as on the nutritive functions, is easily proved. 

 When an animal is bled largely, it is gradually weakened as 

 the flow proceeds, and at last it seems to lose all consciousness 

 and power of movement. If allowed to remain in this con- 

 dition, it seldom or never recovers of itself. But if we inject 

 into its veins, by small quantities at a time, blood similar to 

 that which it has lost, the apparent corpse becomes as it were 

 reanimated, and all its functions are completely re-established. 

 The importance of the red particles is manifestly seen in the 

 effect of this remarkable operation, which is called the trans- 

 fusion of blood ; for if, instead of blood freshly obtained from 

 another living animal, we inject serum without these particles, 

 the effect is but little greater than if so much water were 

 introduced, and the animal dies of the haemorrhage. By this 

 operation, practised on the Human subject, many valuable 

 lives have been saved, that would otherwise have been de- 

 stroyed by loss of blood. Again, if, by mechanical means, as 

 by tying the principal blood-vessel going to any organ, we 

 cause a permanent diminution to any considerable extent, in 

 the quantity of blood with which it is supplied, a decrease in 

 its size is soon apparent, and it may even shrink almost to 

 nothing. On the other hand, we observe that, the more active 

 the function of a part, the larger is the quantity of blood with 

 which it is supplied. Thus, when the antlers of the Stag, 

 which fall off every year, are being renewed, the arteries that 

 supply the parts of the skull from which they spring, are 

 greatly increased in size ; but they shrink again, as soon as 

 the growth of the horns is completed for that year. A similar 

 increase takes place among animals that suckle their young, 

 in the size of the arteries that supply the mammary glands, 

 """by which the milk is formed ; and these also shrink, when 

 this liquid is no longer required. 



