312 BIOLOGY: GENERAL AND MEDICAL 



The interesting researches of Harrison, Burrows, and 

 Carrel upon the growth of tissues in vitro, prosecuted with 

 much zeal during the years 1907 and the present time, 

 have shown that many of the normal tissues of embryos 

 and adults of both warm- and cold-blooded animals can be 

 successfully cultivated in vitro, in homologous plasma. In 

 the embryonal tissues when the tendency to grow is most 

 marked, cultures may be obtained in homologous plasma, in 

 some cases in heterologous plasma, rarely in homologous 

 and heterologous serum, and in a few cases in Ringer's solu- 

 tion; but adult tissues, with limited capacity for growth in 

 comparison, can only be cultivated in homologous plasma. 



Finally, blood relationship has a distinct bearing 

 upon the subject of symbiosis for organisms whose chem- 

 ical affinities are opposed to one another may be unable 

 to become symbionts; and in cases of parasitism, it is 

 conceivable that one of the first adaptations to be acquired 

 by the parasite is tolerance to the physiologico-chemically 

 antagonistic conditions to be found in the body of the host. 

 Indeed, as will be shown in the chapter upon Infection 

 and Immunity, the experimental exaltation of micro- 

 organismal virulence is a matter of overcoming the body 

 defenses, which from the present standpoint may be looked 

 upon as the establishment of a tolerance toward originally 

 antagonistic chemico-physiological conditions. 



REFERENCES. 



GEORGE H. F. NUTTALL: " Blood Immunity and Blood Relation- 

 ship," Cambridge, 1904. 



EDWARD TYSON REICHERT and AMOS PEASLEE BROWN: "The 

 Differentiation and Specificity of Corresponding Proteins 

 and Other Vital Substances in Relation to Biological 

 Classification and Organic Evolution: The Crystal- 

 lography of Hemoglobins." The Carnegie Institution, 

 Washington, 1909. 



MAGNUS and FRIEDENTHAL: "Ueber die Specifitat der Verwand- 

 schaftsreaction der Pflanzen." Berichte der deutschen 

 botanischen Gesellschaft, xxv, 1907, 242; xxiv, 1906, 601. 



Ross G. HARRISON: Proc. Soc. Exp. Biol. and Med. 1907, iv, 140; 

 Jour. Exp. Zool., 1910, ix., 787. 



MONTROSE T. BURROWS: Jour. Amer. Med. Assoc., 1910., Iv, 2057; 

 Jour. Exp. Zool., 1911, x, 63. 



ALEXIS CARREL: Jour. Exp. Med., 1911-1912. 



