CHAPTER XIX. 

 THE CULTIVATION OF TISSUE IN VITRO. 



IT has been shown that the death of the individual 

 (somatic death) among higher animals is soon followed by 

 the death of its parts (molecular death). But when one 

 considers why, it appears that the two stand in relation- 

 ship to one another only in the sense that somatic life is 

 the great source of provision and regulation by which the 

 cells are fed, exercised, and relieved of their waste prod- 

 ucts. Is it because of the loss of oxygen and nourishment 

 and the removal of waste by the once circulating and now 

 stagnating juices that the cells die? If some artificial 

 means could be provided for maintaining the appropriate 

 temperature, admitting the necessary oxygen, supplying 

 the necessary foods, and washing away waste products, 

 could tissues be kept alive indefinitely? 



If life is, as there is every reason to suppose, a physico- 

 chemical manifestation, then, given appropriate condi- 

 tions, it should continue under unnatural conditions, and 

 under inappropriate conditions it ought to cease under 

 natural conditions, which is, indeed, the case. 



To know that a tissue kept under artificial conditions 

 is living, the same criteria must be applied as are used to 

 determine that any supposed living organism is living. 

 It must show signs of life by movement, by multiplica- 

 tion, by metabolism, etc. Not all of the tissues of the 

 body of a highly organized animal are able to show the 

 usual signs of life manifested, for example, by the protozoa. 

 Many of them are so highly specialized and differentiated 

 as to do nothing visible, and nothing by themselves, as 

 in the case of a nerve cell of a sensory ganglion. Many 

 of them belong to tissues whose reproductive power was 

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