62 BIOLOGY OF DEATH 



cells in vitro is tlie fact that in certain lower forms of life 

 a small bit of tissue or even a single cell, may develop in 

 culture into a whole organism, demonstrating that the 

 capacity of morphogenesis is retained in these isolated 

 somatic cells. H. V. Wilson has shown that in coelenter- 

 ates and sponges complete new individuals may develop 

 in vitro from isolated cells taken from adult animals. 

 By squeezing small bits of these animals through bolting 

 cloth he was able to separate small groups of cells or 

 even single cells. In culture these would grow into small 

 masses of cells which would then differentiate slowly into 

 the normal form of the complete organism. Figure 16 

 shows an example of this taken from Wilson's work. 



It was early demonstrated by Carrel and Burrows 

 that the life of the tissues in vitro, which varied in differ- 

 ent experiments from 5 to 20 days, could be prolonged by 

 a process of successive transfers of the culture to an 

 indefinite period. Cells which were nearing the end of 

 their life and growth in one culture need only be trans- 

 ferred to a new culture medium to keep on growing and 

 multiplying. Dr. and Mrs. Warren H. Lewis made the 

 important discovery that tissues of the chick embryo 

 could be cultivated outside the body in purely inorganic 

 solutions, such as sodium chloride, Einger's solution, 

 Locke's solution, etc. No growth in these inorganic cul- 

 tures took place without sodium chloride. Growth was 

 prolonged and increased by adding calcium and potas- 

 sium. If maltose or dextrose, or protein cleavage pro- 

 ducts were added proliferation of the cells increased. 



By the method of transfer to fresh nutrient media. 

 Carrel has been able to keep cultures of tissue from the 

 heart of the chick embryo alive for a long period of 

 years. In a letter, recently received, he says: ''The 



