COLOURLESS CORPUSCLES USES OF RED CORPUSCLES. 209 



mode in which this reproduction is effected has not yet been 

 clearly made out ; but there is strong reason to believe that the 

 red corpuscles are developed from the corpuscles of the chyle 

 and lymph ( 222) which are continually being poured into 

 the circulating current, and of which isolated examples, known 

 as the white or colourless corpuscles, are met with in every 

 drop of blood that is examined under the microscope. The 

 size of these is pretty much the same in all Vertebrata, their 

 diameter being usually about 1 -3000th of an inch. In the 

 blood of Man and the Mammalia in general (fig. 115, D) they 

 are not easily distinguished from the red particles ; their 

 diameter being nearly the same, while the colour of single 

 discs of the two kinds is not very dissimilar. But in the lower 

 Vertebrata, whose blood has large oval red particles, the differ- 

 ence between the two kinds is very obvious ; and the resem- 

 blance which the colourless globuler (c, figs. 116-119) bear to 

 those of the chyle and lymph, i? very striking. Similar colour- 

 less particles exist, to a variaole amount, in the nutritive fluid 

 of Invertebrated animals ; so that in this, as in some other 

 respects, that fluid bears a stronger resemblance to the chyle 

 and lymph of the Vertebrata, than it does to their blood, 

 which is characterised by the presence of the red particles. 



235. Physiologists are now generally agreed, that one of 

 the functions of the Red Corpuscles is to convey oxygen from 

 the lungs to the tissues and organs through which the blood 

 circulates, and to bring back the carbonic acid which is set 

 free in these, so as to deliver it at the lungs. For although 

 it is certain that the liquor sanguinis can also convey these 

 gases, yet experiment shows that the red corpuscles can take 

 up, bulk for bulk, a much larger proportion of them ; and 

 that the blood which is richest in these particles is, therefore, 

 most fit to serve as the medium for the transmission between 

 the respiratory organs and the body at large. Now it is in 

 the nervo-muscular apparatus that there is the greatest demand 

 for oxygen; for this apparatus is not capable of vigorous 

 action, unless oxygen be freely supplied to it. The quantity 

 of this it requires, however, depends upon the exercise of its 

 powers ; for when at rest, it needs little or no more than is 

 made use of by the other tissues ; but whilst in activity, it 

 needs a greatly-increased supply. The quantity of oxygen 

 which the animal takes-in by its lungs, and the amount of 



