EQUIVALENCE OF HEMATOPOIETIC ANLAGES. I. SPLEEN 259 



The recourse to the experimental method may contribute 

 more definite information about mutual relationship of blood- 

 cells as well as about the source of their regeneration and the 

 function of different blood-forming organs. The study of in- 

 tense general destruction of blood tissue through bleedings and 

 of its partial destruction by X-ray application, followed by the 

 study of its regeneration, have already contributed undeniable 

 data. The use of a method known as lympho and myelotoxic 

 intoxication, (I would better say stimulation) may give in this 

 respect most conclusive results. This method was indicated in 

 1901 b}^ Dr. Flexner (17). Specific leucolytic, spleno- lympho- 

 marrow-lytic sera are injected into animals. The consecutive 

 circulation of antibodies present in these sera find adequate 

 receptors in certain cell groups and a proliferation follows as a 

 result of molecular changes in these cells. 



One of the most striking results obtained in experimental 

 pathology of the hematopoietic organs is the myeloid metaplasis 

 of lymphoid tissue. First described by Fraenkel it was experi- 

 mentally obtained by Dominici (10) by producing traumatic 

 anaemias and typhoid infection. Later the myeloid metaplasis 

 of the lymphoid tissue was repeatedly observed during various 

 pathological processes, (anaemia, leukemia, intoxications, infec- 

 tions, tumors) . According to the statements of various investi- 

 gators, the myeloid metaplasis invariably consists in a simul- 

 taneous development of erythro- and leucopoietic or granulo- 

 blastic tissues. This was accounted for by most of the patho- 

 logists as being a proof of a close relationship between these 

 tissues. The common origin of leucocytes and erythrocytes 

 was therefore admitted by many pathologists who formed the 

 so-called dualistic school, which distinctly separated the myelo- 

 blastic (erythro-granuloblastic) tissue from the lymphatic tissue. 

 The present paper has for its main subject the study of a very 

 extensive chiefly granuloblastic (or myeloid) metaplasis of the 

 embryonic mesenchyme, therefore a survey of different opinions 

 concerning the subject may be permitted. 



The myeloid metaplasis was observed chiefly in the spleen, 

 and occasionally mentioned in the lymph-glands and other 



