EQUIVALENCE OF HEMATOPOIETIC ANLAGES. I. SPLEEN 265 



thorough revision of the fundamental problems of hematology. 

 Indeed, if the various anlages of the hematopoietic organs were 

 equivalent and contained idejitical stem cells, hematopoietic 

 organs other than the spleen must have reacted also. Since 

 the structural peculiarities in the different organs of the embryo 

 are not fully differentiated, the reaction of the stem cells in 

 different hematopoietic orga>ns could be expected to be more 

 homogenous. As shown further, the specific intervention was 

 indeed followed by changes both in the spleen and iji all the 

 other hematopoietic organs and the reaction of these different 

 organs was substantially similar. These facts were mentioned 

 and demonstrated by me at the New Haven Meeting. ^ 



The grafting of adult spleen on the allantois of the embryo is 

 a complex intervention. The grafted tissue contains small and 

 large lymphocytes, together with the so-called reticular tissue, 

 and with the vessels and their different layers, all belonging to 

 a full-grown organism. Which of these elements has to be re- 

 garded as the source of the stimulation could not yet be de- 

 fined conclusively. However, there is no doubt the intervention 

 applied introduces in the embryo heterogeneous substances. 



It is known that the organism reacts to the introduction of 

 heterogeneous substances by a production of antibodies and to 

 the introduction of heterogeneous cells by production of the 

 so-called lysins. The erythrolysins which are developed by the 

 immunized animal have a dissolving power on the red blood 

 corpuscles against which the animal is immunized, the leuco- 



^Abstr. Proc. Anat. Record, Jan. 1916. 



In this connection I desire to call attention to the substitution of a reference 

 to Dr. Murphy's last communication (21) on p. 96 of No. 1, vol. 24, Journ. Exp. 

 Med. July, 1916, in my paper on "Differentiation ..." for a footnote, in 

 which I stated: "I wish to express my indebtedness to Dr. J. B. Murphy, who 

 kindly demonstrated to me the method of grafting described in this paper. 

 Murphy, J. B. and Rous, P., 1912. The behavior of chicksarcoma .... 

 Journ. Exp. Med. vol. 15." My paper, which was received for publication in 

 February '16, and published in July '16 could certainly not contain a reference 

 to Dr. Murphy's communication, which received for publication in May, 

 appeared also in July. This alteration seems to me the much the more inap- 

 propriate, because it has been made to apply to the demonstrations given by 

 me at the Anatomical Meeting, 1915. 



