EQUIVALENCE OF HEMATOPOIETIC ANLAGES. I. SPLEEN 303 



of the apparently homogeneous mesenchymal anlage, at the 

 expense of which many different ceils are developed. I cannot 

 enter now into a detailed consideration of this problem. How- 

 ever, the question whether the amitosis may not be looked upon 

 as one of the factors in the differentiation of the living substance, 

 can find its justification. 



Data concerning the general meaning of the myeloid metaplasis 



The results obtained in the embryonic spleen at different 

 stages of its development have a close bearing upon the myeloid 

 metaplasis, well known to the pathologists. What is the general 

 meaning of these changes, and what are their relations to the 

 stimulus applied and to other reactions displayed at the same time 

 by the organism? The specific conditions under which I had 

 to work last winter did not allow me so far to obtain definite 

 data in this respect. However, the study of the experiments 

 made may give a few suggestions concerning the problem. 



There is no doubt the intervention applied introduces in the 

 organism heterogeneous substances. The connection between 

 the introduction of these substances and the changes described 

 above may be conceived in two different ways. Either these 

 substances have general stimulating action on the mesenchyme 

 and on the blood stem cells (as for example the thyroid sub- 

 stance in the experiments of Gudernatsch^ on the develop- 

 ment of tad-pole limbs) ; or the action of these substances may be 

 similar to that of specific antigenes, which introduced in the 

 organism incite the production of antibodies. In the latter case 

 the proliferative reaction exhibited by the blood stem cells may be 

 looked upon as a material basis for the phenomena of immunity. 

 The proliferation in this case would have been brought about 

 by the interaction between specific antigenes and their cell 

 receptors. Only results of new series of experiments will decide 

 which of these two conceptions has to be accepted. 



The analogy between the myeloid metaplasis and the results 

 of the experiments described is obvious. It is important to 



^ Gudernatsch, F. Feeding Experiments on Tadpoles. II, A further con- 

 tribution to the knowledge of organs with internal secretion, Am. Jour. Anat., 

 1914, vol. 15. 



