RED BLOOD-CORPUSCLE&-THEIR ORIGIN. 259 



exactly with the period at which the corpuscles in the 

 blood of man and the mammalia cease to exhibit nuclei. 

 We can only say that we are acquainted with no fact 

 whatever which speaks in favour of a further independ- 

 ent development, or of a cell- division, in the blood, but 

 that everything points to the probability of a supply 

 from without. The only hypothesis which has in more 

 recent times been advanced with regard to the independ- 

 ent development of the blood-corpuscles in the blood 

 itself, is that of Gr. Zimmermann,* who assumed that 

 there were little vesicles present in the blood, which gra- 

 dually grew by intussusception whilst circulating with it, 

 and ultimately constituted the real blood-corpuscles. 

 Now little corpuscles certainly do occur in the blood (Fig. 

 52, A), only, when they are more accurately examined, 

 a peculiarity reveals itself which is unknown in young 

 embryonic forms, namely that they oppose an extraordi- 

 nary degree of resistance to the most different agencies. 

 In their ordinary state they are of a beautiful dark red, 

 the colour being very intense and frequently nearly 

 black ; if they are treated with water or acids which dis- 

 solve the ordinary red corpuscles with ease, it is observed 

 that the little bodies require a very much longer time 

 before they disappear. Upon adding a large quantity of 

 water to a drop of blood, they will be seen to remain for 

 a considerable time after the other corpuscles have dis- 

 appeared. This peculiarity accords best with what occurs 

 in the changes which take place in the blood, when it is 



* Ztmmermann has recently ( Archiv f. path. Anat. und Phys.,' vol. xviii., pp. 

 221-242) given us a more explicit statement of his views, and from it we gather 

 that he considers the blood-corpuscles to originate in small, colourless vesicles 

 which are introduced from the chyle into the blood and may be seen in it when its 

 fluidity has been preserved by means of salts. But probably these vesicles are only 

 artificial products, similar to those described nearly ten years ago by Harting 

 ('Nederl. Lancet,' 1851, 3d ser.^lst Jaarg., p. 224). From a MS. Note by the 

 Author. 



