A. TYLER 355 



kidney were injected into hen's eggs at 2/2 to 8 days of incubation. 

 However, Weiss ( 1953b, 1955 ) more recently considered this 

 to be due to hemorrhage caused by vascular damage rather than 

 to specific stimulation of growth by the antisera. 



Apart from the above-mentioned work, experiments on the 

 effects of antisera on development deal with inhibitory effects. 

 Much of the current work in this field has been summarized by 

 Nace (1955). In most cases the antisera have been prepared 

 against rather complex extracts, and the various inhibitory eflFects 

 are not readily interpretable in specific terms. Perhaps the best 

 examples of specific action of antisera on embryonic tissues stem 

 from the discovery that destruction of fetal blood cells in human 

 cases of hemolytic disease of the newborn was due to the action 

 of an antibody produced in the mother in response to isoimmuni- 

 zation with fetal antigen (Levine and Stetson, 1939; Levine et al., 

 1941). This discovery has led to the identification of a large num- 

 ber of human blood cell antigens ( see Levine, 1954 ) in addition 

 to the now well-known Rh factor ( Landsteiner and Wiener, 1940 ) 

 and its variants that were concerned in the original observations. 

 The action of the antisera is evidently specifically on the fetal red 

 cells, other clinical and pathological features of the disease be- 

 ing referable to blood cell destruction ( Levine et al., 1941 ) . This 

 is, then, a selective action of an antiserum on a tissue of the de- 

 veloping organism and one in which much is known, at least 

 genetically, about the particular antigens involved. Unfortunately 

 embryological studies in this field have not kept pace with the 

 genetic, ethnological, and technical advances. This is understand- 

 able by virtue of the relative inaccessibility of the material. The 

 Rh factor has been demonstrated in a 5-cm fetus ( Stratton, 1943; 

 cf. Levine, 1948). However, the effects of isoimmunization ap- 

 pear to be exerted on the almost fully developed fetus or on the 

 newborn infant. There is, of course, uncertainty as to just when 

 the antibodies are produced and reach the fetus in effective con- 

 centration. Experiments with lower mammals in which similar 

 isoimmunization has been reported (see Coombs, 1949; Kellner 

 and Hedal, 1953) may be expected to provide more information 

 of embryological significance. 



