288 BIOLOGY. [BOOK in. 



capable of engendering by segmentation other hsematia similar 

 to themselves. 



In the animal, moreover, the histological multiplication by 

 scission, by segmentation, is scarcely observable, except in 

 elements not much differentiated ; for example, in the haematia, 

 the leucocytes, the epithelial cells. The superior histological 

 elements, the nervous cell, the muscular fibre-cell, are never 

 segmentised. 1 



When segmentation is observable, it is produced only in 

 elements fully developed, adult in some fashion. The small 

 nuclei, the small cells are not segmentised. In truth, in every 

 anatomical element growth has two phases : the first, during 

 which the element augments! merely in volume ; the second, 

 during which it multiplies. Both of them have equally as cause 

 an excess of assimilation. But in order that the second may be 

 produced, the anatomical element must naturally have attained 

 its limit of growth, and can no longer assimilate into its sub- 

 stance molecules of new formation. 



In the adult vertebrate, the genesis of the white globules, the 

 leucocytes, is especially produced in the lymphatic ganglions ; 

 and in the sanguineous closed ganglions, the spleen, for example. 

 Kecent observations have shown that the venous blood coming 

 forth from the spleen is much richer in globules than the arterial 

 blood entering it. 



There is great probability that the new red globules proceed 

 simply from the modification, the transformation of the white 

 globules. Thus, the venous blood of the spleen contains numerous 

 globules intermediate between the leucocytes and the hse- 

 matia. These mixed forms are met with also in great number 

 in the blood after a haemorrhage, or frequent bleedings, when the 

 sanguineous liquid is in process of regeneration. 



We have previously cited a curious fact observed by Burdach, 

 the coloration into red of a lymphatic clot. Analogous facts 

 have been noted by Yirchow and Friedreich. These physiologists 

 have likewise seen the lymph redden in the air. 

 1 Ch. Robin, TUd. 



