SECT. 2] 



AND WEIGHT 



461 



culture. Would small pieces of it be found to grow in tissue culture 

 proportionately to the growth of the organism as a whole, or is the 

 growth-rate a value absolutely dependent on the intactness of the 

 embryo? This question has found a definite answer in the re- 

 markable work of Cohn & Murray, who, following up a few pre- 

 cursory experiments of Carrel, removed hearts from chick embryos 

 from the 4th day onwards, made 



1-0 

 Days 5 



J I L 



l—J I 1 ¥ J 



dw 

 db 

 W 



cultures of them in adult hen 

 plasma or plasma plus Ringer 

 solution, and determined their 

 rate of growth. This was done 

 by four methods : {a) subtract- 

 ing from the total area of tissue 

 after n days of cultivation the 

 area of the central portion, 

 {b) dividing the area of growth 

 made (total minus central por- 

 tion) by the size of the original 

 fragment, {c) dividing the area 

 of growth made by the size of q 

 the central portion at the time 

 of measurement, and [d) divid- 

 ing the area of growth made 

 by the square root of the area 

 of the central fragment. With 

 these methods and carefully 

 controlled conditions they found that the growth-rate of the cultures 

 of embryo heart fell in an exactly parallel manner to the Minot curve 

 previously found by Murray to hold for the chick. Figs. 62 and 63, 

 taken from Cohn & Murray's paper, show this fall, and may be 

 compared with Fig. 34 which shows the corresponding Minot curve 

 for the whole embryo. The kink in the heart culture curve may perhaps 

 be related to special changes occurring in the organ at the 9th day (see 

 Section 23). It must be remembered that the heart of the chick has 

 been stated by Schmalhausen to grow at the same rate as the whole 

 body, though, as a reference to Table 56 shows, the Schmalhausen 

 Cvt is 276 for the heart and 321 for the whole body. However, it 

 would not have been material which organ had been selected by 

 Cohn & Murray, for all organs have growth-rates either descending 



6 7 8 9 10 11 12 13 14 15 16 

 Incobation age 



Fig. 63. 



