412 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



against the individuality differential of a particular tumor. This is indicated 

 also by the observations of Rous and Murphy that the immunity noted after 

 retrogression of three types of chicken sarcoma, namely, a spindle-cell sar- 

 coma, an osteochondroma, and a rifted sarcoma, was directed mainly against 

 the special kind of tumor that had retrogressed. It appears moreover that 

 different types of tumors differ quantitatively in the degree of immunity they 

 produce, and the effectiveness of the immunization seems also to depend 

 on the place where the first and second tumors were inoculated. Thus, in 

 the rabbit each tumor of the uterus and mammary gland seemed to differ 

 in certain respects from the Brown-Pearce rabbit tumor, in experiments 

 reported by Appel, Saphir and their collaborators, and by Cheever and 

 Morgan, and by Greene. Furthermore, there is even the possibility that 

 immunity against a tumor of a different species is not absolutely specific, but 

 that it may extend also, although to a lesser extent, to individuals belonging 

 to a nearly related species. 



(4) Immunity produced through inoculation of pieces of normal tissue or 

 of tumor tissue unable to induce tumor formation. 



Ehrlich obtained immunization against a mouse carcinoma by first inocu- 

 lating mice with pieces of a hemorrhagic mouse carcinoma, which itself 

 did not give rise to tumor formation because the tumor cells were injured. 

 This experiment suggested the use of normal tissues for purposes of immuni- 

 zation. Bashford, by injection of homoiogenous defibrinated blood, obtained 

 active immunity against subsequent inoculations with homoiogenous tumor, 

 and Schoene found that other living tissues, in particular, embryonal tissues, 

 were similarly effective. These observations were subsequently confirmed 

 and extended by many investigators. The results obtained may be summarized 

 as follows: (a) Only living tissue is effective in inducing immunity; dead 

 cells do not immunize, (b) It is the organismal differentials of the inoculated 

 pieces which give rise to this type of immunity. There must be a definite 

 relation between the organismal differential of the piece of tissue serving 

 as antigen (vaccine) and that of the host; furthermore, the organismal 

 differential of the antigen must bear a definite relation to the differentials 

 of the tumors against which the immunization is directed. Autogenous 

 tissues do not, therefore, act as an efficient antigen (Apolant, Woglom). 

 Tissues which possess homoiogenous differentials in reference to the host 

 animals, immunize against homoiogenous tumors, and heterogenous tissues 

 immunize against tumors possessing the same heterogenous differential. 

 However, it is possible that an immunization may in certain instances be 

 produced also by the use of tissues from nearly related species, mouse 

 tissue immunizing against a rat tumor and vice versa; but this immunity, 

 if successful at all, is much weaker than that produced by tissues with 

 identical organismal differentials, (c) Different types of tissues differ as 

 to their effectiveness as antigens ; embryo skin is very effective, whereas 

 cartilage, bone, muscle tissue, lens and brain are not. Other tissues range 

 between these extremes. That cartilage, bone and muscle are relatively 

 unfavorable may be due to the predominance, in these tissues, of inter- 



