Cultivation of Tissue in Plasma from Alien Species. 125 
those just described. Pieces of rat spleen or tumor when trans- 
ferred to rat plasma after five or six days in human plasma begin 
to grow very actively. The cells, however, often present extremely 
ragged outlines. Giant cell formation may be noted after the 
transfer. 
The growth of rat sarcoma in pigeon plasma is especially beau- 
tiful and appears to be quite characteristic. During the first four 
or five days there is a progressive radial extension of large clear 
spindle cells of strikingly uniform size and morphology. The 
strings of cells are connected by long slender processes. Fine 
granular fat accumulations in the protoplasm appear early and 
increase in size and number with the age of the specimen, just as 
occurs in rat and guinea pig plasmas. As a rule no further 
growth takes place after the fifth day, and the cells at this time 
begin to show signs of disintegration. Intact well stained nuclei, 
however, may sometimes be seen in preparations eight or nine 
days old. Transfer of the pieces of tissue in four-day specimens 
to fresh pigeon plasma does not result in a prolongation of the 
period of activity. 
In summarizing the above findings we notice that goat plasma 
is the only medium used in which there was no growth; in dog 
plasma growth was of short duration. Arranged in the order of 
suitability we have guinea pig, rabbit, pigeon, human, dog and 
goat. In a study of cytolysins for rat and mouse tissues we found 
that hemolysins were present in human, dog and goat sera. The 
sera tested were taken from animals from which plasma had been 
obtained for tissue cultivation. We have found also that in plas- 
ma from guinea pigs immunized against rat corpuscles, growth of 
rat sarcoma does not occur, or is of an abortive character, and 
that there is a similar inhibition of growth in plasma from guinea 
pigs previously treated with large doses of rat sarcoma. 
