no CICATRIZATION OF WOUNDS 



However, it will certainly be fruitful in the hands of the new 

 generation of biologists. 



Besides the fundamental classical problems which can be 

 attacked, this method will certainly reveal, and has already 

 revealed, new problems which otherwise might always have 

 remained ignored. I shall illustrate this statement by two 

 suggestive examples. 



We have seen that the fragments of muscular tissue, removed 

 from the heart of a chicken embryo, frequently continue to 

 beat in the culture. Fisher made the following remarkable 

 experiment. 



If two palpitating fragments, proceeding from the same 

 heart, are put next to each other, but v/ithout touching, one 

 usually observes that their rhythm is not identical. One frag- 

 ment beats eighty times a minute, for instance, the other fifty. 

 If it so happens, which is rare, that their pulsations are identi- 

 cal, they are nevertheless not synchronous. But these frag- 

 ments proliferate and gradually surround themselves with a 

 circle of new cells which penetrate into the medium in the 

 shape of a thin, translucid, living layer. After a certain length 

 of time these membranes issued from the two fragments come 

 into contact. At that very moment, the rhythm becomes 

 identical. The synchronism is re-established; the two frag- 

 ments beat as one. 



The bird has been long dead; the small pieces of muscle 

 separated from its heart have neither blood circulation nor a 

 nervous system connected to a main trunk, and yet they seem 

 to recognize each other as soon as they come in contact. They 

 persist in accomplishing the work for which their cells were 

 created, not in a haphazard independent fashion but together 

 and co-ordinately. Needless to say, there is not the beginning 

 of an explanation for this curious phenomenon. 



Another example: a single isolated cell does not proliferate 

 by mitosis. It cannot reproduce and dies without offspring, 

 even though it appears to be identically in the same conditions 

 as the healthy culture from which it has been separated and 

 the ceils of which prohferate rapidly. Cellular growth and 



