I08 CICATRIZATION OF WOUNDS 



of heart, rapidly surrounded by a transparent and fragile circle 

 of new cells, often continue to beat during two or three weeks, 

 sometimes longer. They can be seen through the microscope, 

 contracting spasmodically, and nothing is more impressive 

 than to observe this fundamental and marvellous mechanism 

 which is still so mysterious. This famous experiment gave 

 rise to the legend of the 'ever-beating heart'. But there is no 

 example of these heart fragments having beaten for more than 

 three months. A month is already a limit rarely attained. 

 The beats become more and more distant as the culture ages, 

 and generally last only from fifteen to twenty days. The con- 

 tracting muscular cells are progressively replaced in the culture 

 by inert cells of conjunctive tissue, the fibroblasts, whose 

 reproductive energy is greater and which finally reign alone. It 

 must not be forgotten that at the end of fifteen days the initial 

 fragment has been cut seven times and that after each division 

 it has reconstituted itself mainly with fibroblasts. At the end 

 of a fortnight, the beats are already much weaker and some- 

 times only perceptible every ten seconds. They often cease 

 altogether when the culture is examined under the microscope, 

 and the temperature must be raised — for instance, by placing 

 the whole microscope in a small incubator — in order to see 

 them reappear. 



Tissue-culture is neither simple nor easy if one wishes to 

 maintain pure strains in good health for any length of time. 

 The technique has been so marvellously perfected by Carrel 

 that it is easy to keep them alive during two or three weeks. 

 The difficulties come later, and it requires a long experience 

 to be able to prolong their existence beyond three months. It 

 even seems as if the difficulties increased with age. This 

 explains the fact that the only laboratory where cultures have 

 been kept alive for twenty-four years is that of Dr. Carrel, 

 which is splendidly organized and has several 'culture doctors'. 



For cultures, Hke human beings, often have slight illnesses. 

 These must be known and the consequences attenuated or 

 annulled. A fatty degeneration shown by the apparition of 

 small refractive globules, or a variation in structure, is an 



