THE BLOOD AND THE LYMPH. 721 



it, it is perhaps impossible to suppose that they ever become blood-cells. 

 This being established, it is a question whether the change of the blood- 

 cells, their formation and their dissolution, is not perhaps muoh slower 

 than is commonly assumed, and whether they are not elementary parts 

 of a more stable nature than is supposed. I am unable to throw any 

 decided light upon this point, and will merely remark that in any case, 

 so long as the growth of the body goes on, and the quantity of blood is 

 augmented, an energetic formation of blood-cells must take place; in 

 opposition to which it is quite unascertained whether, in this period of 

 life, blood-cells are dissolved ; on which account, also, it cannot be 

 stated how many of the elements of the chyle undergo the metamor- 

 phosis into blood-corpuscles. In the adult, only this much should be 

 regarded as certain, that when from any cause the quantity of blood 

 has become diminished, it may be replaced together with the red blood- 

 cells ; whilst it is altogether unascertained whether, under the usual 

 conditions, anything like an energetic solution and re-development 

 of those cells takes place. As their formation cannot be definitely ob- 

 served, nothing remains by which the question can be decided but 

 observations respecting the dissolution of the blood-globules; these ob- 

 servations, however, have by no means tended to demonstrate the occur- 

 rence of a constant change of the elements of the blood, taking place at 

 short intervals ; for although in the spleen of many animals a vast 

 quantity of blood-globules undergoing disintegration is met with, the 

 frequent and regular recurrence of a dissolution of those bodies in that 

 organ has not yet been proved. Taking everything into consideration, 

 I am therefore of opinion, that the question as to when, and to what 

 extent, blood-corpuscles perish and are again formed in the adult, can- 

 not be definitely decided from the facts at present in our. possession, 

 although I am inclined to think that the elements of the blood are not 

 altogether such perishable structures as is commonly believed. 



I have still to mention, that, quite recently, the view that the blood- 

 globules are formed independently in the blood, out of colorless cells, is 

 advocated by various authorities. Lehmann and Funke rely, the for- 

 mer on the large amount of colorless cells in the blood in the hepatic 

 veins, the latter on the similar condition of the blood in the splenic vein, 

 and they both consider it probable, that a new formation of red blood- 

 cells takes place within the bloodvessels of the liver and spleen. It 

 appears to me, that this question must be approached with very great 

 care, so long as the transition of the colorless cells into blood-corpus- 

 cles has not been directly observed, which in this case has by no means 

 been done. At present we are far too little acquainted with the vital 

 relations of the colorless cells in the blood to conclude, merely from 

 their existence, upon a formation of red blood-cells, and especially when 

 we remember the facts stated; since, as I have elsewhere shown ("Mikros. 



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