282 E. V. Cowdry, 



investigations on the disappearance of mitochondria in red blood cells 

 '11, p. 495, and Firket's in epidermal cells '11, p. 544). On this hypo- 

 thesis newly formed platelets would probably contain mitochondria, while 

 older ones would not. 



On the. other hand it may depend upon the mode of origin of the 

 platelet; upon whether or not the budded off cytoplasm of the mega- 

 karyocyte (Wright ' 10, p. 270) or the lymphocyte (Kyes personal communi- 

 cation) contains mitochondria. This is supported by my observation (p. 11) 

 that the mitochondria in lymphocytes may be either restricted to the 

 cytoplasm immediately surrounding the nucleus or else be distributed 

 evenly thoughout the cytoplasm, even extending into the pseudopod- 

 like prolongations. 



These conceptions are not mutually exclusive. In all probability 

 both the age of the platelet and its mode of origin are factors 

 influencing the presence of mitochondria in it. 



My observations on the mitochondria of the coarsely granular 

 leucocyte (eosinophile) are supported by Meves' statement ('10, p. 656) 

 that mitochondria are either very rare, or else entirely absent, in the 

 eosinophile leucocytes of the salamander. I do not consider that my 

 observations with janus green are in any sense final. Further refine- 

 ments in technique will be necessary before definite assertions can be 

 made relative to the amount of mitochondria in eosinophiles. 



The problem of mitochondria in the mastleucocyte is beyond the 

 scope of my present methods of vital staining. It is pure speculation. 

 Investigators are divided into two camps with regard to this cell. 



Those who hold with Minot ('12, p. 518) and others that it is a 

 degenerating form would doubtless be inclined to believe that mito- 

 chondria are absent, in view of the abundant evidence at our dis- 

 posal that mitochondria become reduced and finally disappear in the 

 later stages of the life of the cell (see Meves '11, p. 495 and Firket 

 '11, p. 544). 



Those, on the other hand, who look upon these leucocytes as 

 being in an active stage of cytomorphosis (Maximow '13, p. 287) would 

 regard the occurrence of mitochondria in them as extremely probable. 



