lO MAMMALIA. 



when freshly -drawn is of a uniform appearance ; if it is allowed to stand, 

 a dark red mass called the clot rises to the surface, the fluid below, 

 named scriivi, becomes colorless. This process of coagulation occupies 

 about twenty minutes, and during it a peculiar odor is emitted. The 

 upper part of the clot is covered with a film of fibrous matter called 

 fibrin ; the remainder consists of myriads of small, round bodies called 

 corpuscles, which can be readily seen by examining a drop of blood under 

 the microscope. These blood corpuscles are circular in the Mammalia, 

 while in the other Vertebrates they are elliptical, and even in the class 

 of Mammalia the distinction between the blood of the various orders is 

 so marked as to .enable a practised eye to indicate the kind of animal 

 from which it has been taken. 



Under the microscope the blood corpuscles are seen to consist of two 

 classes, red and colorless corpuscles; and Huxley writes, "The inverte- 

 brate animals which have true blood corpuscles, possess only such as 

 resemble the colorless corpuscles of man. The lowest vertebrate ani- 

 mals possess only colorless corpuscles. Vertebrate animals, the young 

 of which are born from eggs, have two kinds of corpuscles, colorless ones 

 and red ones, oval in shape and possessing a nucleus. All the animals 

 wh'ch suckle the young (the Mammalia) have, like man, two kinds of 

 corpuscles, colorless ones and small colored corpuscles, the latter being 

 always flattened and devoid of any nucleus. They are usually circular, 

 but in the camel tribe they are elliptical. In the vertebrate series the 

 colorless corpuscles differ much less from one another in size and form 

 than the colored. The latter are smallest in the little musk deer, in which 

 animal they are about a quarter as large as those of a man. On the 

 other hand, the red corpuscles are largest in the Amphibia, in some of 

 which animals they are ten times as long as in man." The blood is the 

 product not of one organ, but of all ; and it is profoundly affected by the 

 circumstance that everv part of the body takes something from the blood 

 and pours something into it. " The blood mav be compared to a river, 

 the nature of which is determined by that of the head-waters, and by 

 that of the animals which swim in it, but which is also much affected by 

 the soil over which it flows, b}^ the water-weeds which cover its banks, 

 and by affluents from distant regions, by irrigation works which are sup- 

 plied from it, and by drain-pipes which flow into it." 



We have gone somewhat fully into detail respecting the blood, 

 because " the Blood is the Life." 



