ORIGIN AND MULTIPLICATION OF RED CORPUSCLES. 129 



with a strong saline solution, were emptied of their contents, like ordinary 

 blood-discs. It is not at all improbable, that both these methods of multi- 

 plication may be followed ; and it can scarcely be doubted that, by one or 

 both, a continual succession of Red corpuscles is kept up. That the corpus- 

 cles may be generated with great rapidity under peculiar circumstances, will 

 hereafter appear (Chap. XL, Sect. 6) ; and their amount may undergo a rapid 

 diminution also, without any evident abstraction of them from the circulating 

 fluid. This diminution seems to be traceable in some instances to a too low 

 specific gravity of the serum ; which will cause the Red corpuscles to rupture 

 by endosmose, just as when they are treated with water. Appearances have 

 been seen by Wagner, Gulliver, and others, in the blood of Batrachia, which 

 might seem to indicate that the Colourless corpuscles ( 151) serve as the 

 nuclei of cells, which, when fully developed, may become Red blood-discs ; 

 but in the Mammalia, it is scarcely possible to imagine that this can occur ; 

 since the diameter of the colourless corpuscles is very constant ; whilst that 

 of the Red blood-discs is so variable, that the former, though sometimes the 

 smaller, are in other instances far larger than the latter. If it be admitted 

 that the Red corpuscles have the power of reproduction, like other isolated 

 cells, it does not seem necessary to seek elsewhere for the source of their con- 

 stant renewal ; and various facts, hereafter to be stated, appear to the Author 

 strongly indicative of the entire functional as well as structural difference, 

 between the red and the colourless corpuscles of the blood of Vertebrata. 



149. That the Red blood-discs, when first formed in the embryo, have an 

 origin common to that of all other tissues, cannot be doubted. They are pro- 

 duced, in the embryo of the Bird, in the portion of the germinal membrane 

 which afterwards becomes the area vasculosa ; this consists of delicate cells 

 very uniformly disposed: and whilst capillary vessels are being formed by 

 the union of the cavities of these, blood-discs seem to be developed from 



Fig. 29. 



Production of blood-corpuscles in Chick, on the fourth day of incubation ; a, particles fully formed ; 

 b. particles in progress of formation; c, similar particles altered by dilute acetic acid, so as to display their 

 nuclei. 



the granules or cell-germs they contain. These changes take place about the 

 second or third day of incubation ; but it is not until some days afterwards, 

 that the discs assume their characteristic form. 



a. Mr. Macleod gives the following history of the development of the blood-corpuscles 

 in the Chick. In blood withdrawn from the heart, on the third day, and diluted with se- 

 rum, or from the germinal membrane or allantois, and diluted with fluid albumen, " a num- 

 ber of small granules are seen floating about the field : these enlarge and become clearer in 

 the centre ; this enlargement goes on very rapidly, and when they have gained to about twice 

 their original size, the central clear part becomes dull. 'jhis dullness slightly increases, and 

 in a short time it is seen to be distinctly granular; whilst the borders are observed to be 

 well-defined, smooth, and clearer than the central part. The enlargement of these bodies, 

 with the granular appearance of their centre, seems not to depend on the aggregation of 

 granules round a centre one, but on a property which they have in themselves of enlarging 

 and presenting that figure. During all this time they are quite spherical and of good con- 

 sistence, as they do not lose their form by considerable pressure. In the second stage, the 

 central portion gradually becomes less opaque, and ceases to appear granular, the external 



