576 Anatomy^ Physiology, and Pathology of the 



In vertebrated animals the blood is of a red colour, but it is 

 colourless in the invertebrated. While circulating it not only 

 appears to be red, but of a homogeneous character; however, on 

 investigating it after being removed from the vessels, it is found to 

 be composed of dissimilar parts. Its chief components are four — 

 fi brine, albumen or serum, corpuscules, and salts; and each of these 

 contributes to the maintenance of the varied functions of the body. 

 The redness of the blood is owing to the presence of red par- 

 ticles or corpuscules, a fact which is demonstrated by their removal, 

 when a colourless fluid, the liquor sanguinis, remains behind. 

 Thousands of these bodies exist in a few drops of blood, and conse- 

 quently they are so minute as to require the aid of the micro- 

 scope to detect them. It was formerly supposed that the vessels 

 in many parts of the system, of which those of the eye were ad- 

 duced as an example, did not contain red corpuscules ; modern 

 research has, however, disproved this position ; and the true ex- 

 planation of the white appearance of the eye is, that its vessels 

 are so small as not to transmit a sufficient number of these cor- 

 puscules at one time, to give colour to the circulating fluid. We 

 have frequent means of ascertaining this, for when inflammation of 

 this organ takes place, these minute vessels are then enlarged, 

 and consequently the red particles, entering in greater numbers, 

 colour the fluid. Hence the cause of the " blood-shot eye." 

 The microscope, as before stated, is necessary to develop the 

 existence of the red particles, and when 

 •^^^' ^* thus examined they are found to be flat- 



tened discs, of a round form (see fig. 3), 

 varying in size from the 4500th to the 

 2800th of an inch. We may state their 

 average size as being near to the 3000th 

 of an inch. Bulk of animal seems not 

 to influence their dimensions, and they 

 differ but little in this respect if taken 

 from the elephant or the mouse. As a 

 rule, they may be said to be small in 



These figures represent the blood- .ittv,- ^T li -^i 



discs of the ox, highly magni- the Herbivorous Maunnal, larger m the 

 sSnTt'^how't^^eiftr^" Carnivorous, and largest in Omnivorous. 

 They are of greater specific gravity than 

 the other constituents of the blood, and hence, when blood is kept 

 in a fluid state, after being drawn, they will be found to sink 

 towards the bottom of the vessel, and thus tend to give that 

 peci:ftiar appearance which is called its buffy coat or inflammatory 

 crust, for the blood in general is longer in clotting when inflam- 

 mation exists. The red particles are intimately connected with 

 the health, strength, and vigour of an animal ; and are found in 

 fewer numbers in ill health. Wild animals are said to possess 



