426 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



nent role in the mechanism through which immunity affects the tumor. He 

 believes that immune processes may act on a tumor injuriously by interfering 

 with the formation of the specific stroma which the tumor needs, and that in 

 this way the growth of a carcinoma may be prevented in immune animals. 

 However, it is much more probable that in his experiments the immune proc- 

 esses acted primarily on the tumor cells directly, diminishing their growth 

 energy, and that as a result of this interference the relations between the tumor 

 parenchyma and the ingrowing connective tissue were changed. We have found 

 in other instances definite correlations between the parenchyma and stroma, 

 in which the condition of the. former was the primary and decisive factor 

 which determined the condition of the latter. 



In the case of microorganisms there is good reason for assuming that the 

 reticulo-endothelial tissue is the seat of the production of immune bodies, 

 and there are strong indications that also the immunity against tumor trans- 

 plants, as far as it is caused by differences in the organismal differentials be- 

 tween host and transplant, is due to a stimulation of the reticulo-endothelial 

 system ; the activity of the lymphocytes and polymorphonuclear leucocytes 

 are apparently factors of secondary importance in the mechanism underlying 

 this immunity ; they function mainly as indicators of the relationship between 

 the organismal differentials of host and transplant. Various investigators, 

 Apolant, Uhlenhuth, Vorlander, Caspari, have assumed that it is the reticulo- 

 endothelial system which gives origin to tissue immunity. In the reticulo- 

 endothelial tissues abnormal cells or strange colloidal substances circulating in 

 the bodyfluids are held back and phagocytosed, and here, especially in the 

 spleen and bone marrow, they set in motion the mechanisms leading to the 

 production of immunity. The main evidence for the conclusion that this applies 

 also to immunity against transplanted tumors consists in the demonstration 

 that different types of this immunity, such as concomitant and retrogression 

 immunity, and probably also certain instances of natural immunity, can be 

 abolished by inactivation (blockade) of the reticulo-endothelial system, either 

 by injection of substances such as India ink, colloidal metals or dyes (Roskin, 

 Lignac and van de Borne), or by means of strong doses of X-rays. Weak doses 

 of X-rays, or certain other procedures, such as stimulation of the spleen 

 through ultraviolet rays (Roskin), may stimulate the reticulo-endothelial cells 

 and thus produce an opposite effect, leading to an increase in immunity against 

 tumor transplants. There is the possibility that in addition to the formation of 

 the immune substances the reticulo-endothelial cells may be concerned in the 

 production of the primary preformed substances circulating in the bodyfluids 

 which act on organismal differentials, although such a function has not yet 

 been demonstrated. Quite recently Ehrich and Harris have found evidence 

 that also local lymph glands may participate in the production of antibacterial 

 immune substances and of immune hemolysins and they noted that such lymph 

 glands show a hyperplasia of the lymphocytic tissue. This observation sug- 

 gests the possibility that it may be the lymphocytes rather than the reticulo- 

 endothelial cells which produce these substances. We would then have to 

 assume that the lymphocytes react to strange differentials in a twofold way, 

 namely by movements and by the production in immune substances. 



