MIRACLES OF SCIENCE 



The fragments of tissues are removed by rapid 

 incision from the organs of animals recently killed, 

 or the bodies of which have been kept in cold storage. 

 The transfer of this tissue to the medium in which it 

 is to grow must be made quickly, as exposure to the 

 air for more than a few seconds may cause the death 

 of the cells. The culture medium consists chiefly of 

 blood plasma, which may be variously modified to 

 test the influence of different chemicals on the growth 

 of different types of cells. 



The tissue i'n its glass receptacle is placed in an 

 incubator, kept at body temperature, from which it 

 may be from time to time removed for examination. 



The growth of the cells may be obvious to the naked 

 eye through the increasing size of the original frag- 

 ment; and it may be more specifically observed under 

 the microscope. In the latter case the microscope is 

 mounted on a heated receptacle so that injury may 

 not be done to the growing tissue by prolonged sub- 

 jection to altered temperature. 



It is curious to note, however, that whereas ex- 

 posure to ordinary room temperature for a period of 

 half an hour or so would destroy the tissue, it may be 

 placed in cold storage for a good many hours, or even 

 days, without permanent loss of vitality. Apparently 

 freezing interrupts the chemical changes and brings 

 about a virtual rest of the cells. Of course chemical 

 action is not absolutely stopped, but it is so much re- 

 tarded that the destructive changes that would occur 

 at ordinary temperature in the course of a few min- 

 utes may be delayed for hours or days. 



We noted that the tissues for cultivation under 



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