ORIGIN OF BLOOD-CORPUSCLES LfMPH. 191 



of complete division. At this early period it is therefore 

 certainly allowable to regard a blood- corpuscle as en- 

 dowed with qualities which are propagated from the first 

 series of cells to the second, and from this to the third, 

 and so on. 



In the blood of a fully developed human being, nay 

 even in that of a foetus in the later months of pregnancy, 

 these phenomena of partition are no longer known, and 

 not a single one of the facts which can be adduced from 

 the history of development speaks in favour of an increase 

 of the cellular elements taking place in fully developed 

 blood by means of direct division, or any other formative 

 process taking its rise in the blood itself. As long as the 

 possibility was regarded as demonstrated, that cells might 

 arise out of simple cytoblastema by means of the direct 

 precipitation of different substances, so long was it pos- 

 sible to conceive new precipitates as forming in the liquor 

 sanguinis from which cells were produced. But this 

 view also has been abandoned. All the morphological 

 elements of the blood, whatever may be their nature, are 

 at present considered to be derived from sources external 

 to the blood. On all hands recourse is had to organs 

 which do not communicate with the blood directly, but 

 rather by the means of intermediate channels. The 

 principal organs which here come into play are the 

 lymphatic glands. Lymph is the fluid which, whilst it 

 conveys certain substances to the blood which come from 

 the tissues, at the same time brings along with it the 

 corpuscular elements out of which the blood-cells con- 

 tinually recruit their numbers. 



With regard to two of the constituents of the blood, 

 there can, I think, be scarcely any doubt but that this is 

 the view which is perfectly warranted, I mean with 

 regard to the fibrine and the colourless corpuscles. As 

 for the fibrine, the properties of which I brought to your 



