1 64 LEO LOEB. 



individual specific but not even species specific. This applies for 

 instance to the growth substances emanating from the corpus 

 luteum in which I found the absence of the individuality differ- 

 ential. The lack of the species differential applies to growth sub- 

 stances extracted from the placenta, to the growth substances 

 which determine the formation of the lens, to substances inducing 

 metamorphosis in amphibia and compensatory hypertrophy in 

 mammals ; it applies to the common hormones of the adrenal gland 

 and thyroid. 



In this case we have to deal with relatively simple substances, 

 some of which are apparently of a lipoid nature, while others are 

 of a still simpler composition. On the other hand we have every 

 reason to assume that the individuality and species differentials 

 are proteid substances or at least that they occur only in combina- 

 tion with proteid substances. 



In the case of the tissue coagulins we have found that the spe- 

 cies differential of the tissues interacts with an adapted substance 

 in the body fluids. In a similar way we find in general an adap- 

 tation between body fluids and cells which is based on the pres- 

 ence of the individuality and spe?ies differentials. It can be 

 demonstrated directly in the case of the natural hemolysins, but 

 probably applies as we have pointed out above, to the relations of 

 all tissues to body fluids. It exists, as we 'found recently, even in 

 the case of invertebrates where we established the interaction of 

 species differentials in the case of the experimental amcebocytic 

 tissue and the blood serum. We shall refer to it again later. It 

 also applies to the relation between the antigens and immune 

 substances. 



SUPPLEMENTARY DIFFERENTIALS IN BODY FLUIDS. 



In all those cases the individuality or species differential of the 

 tissues interacts with an analogous substance in the body fluids. 

 It is, however, not certain that the substance or group in the body 

 fluids is identical with that in the tissues, although they fit into 

 each other specifically. A difference between the two could be 

 demonstrated in the case of tumor immunity. While species im- 

 munity can be produced with body fluids as well as with tissues 

 of a certain species, individuality immunity can only be produced 



