66 PROTOPLASM 



eating this environment so that cells could be grown and studied 

 outside the animal body in comparable surroundings. Attempts 

 to accomplish this were made many times and in a number 

 of ways. The first efforts involved the isolation of entire organs 

 from the body. These were simply kept alive in solutions, no 

 growth taking place. The English physiologist Ringer found 

 (in 1880) that the heart of the frog when perfused with a salt 

 solution (of sodium, potassium, and calcium chlorides) would 

 continue to beat for some time after its removal from the body. 

 The German Ludwig artificially circulated a fluid through the 

 blood vessels of an excised organ and thus obtained the survival 

 of glands for a number of hours. Modern methods have revived 

 this older technique in a much improved form. With the aid of 

 a carefully controlled pump, a respiratory chamber, and aseptic 

 conditions, parts of the body perfused with a nutrient fluid can be 

 kept alive outside the body for several weeks. But such methods, 

 though of great value to general physiology, are too gross to 

 permit the study of individual cells. 



Knowledge of the living cell has been greatly augmented by 

 studies based on the technique known as tissue culture, which is 

 the cultivation of cells and tissues in vitro (literally "in glass" 

 but meaning "outside the organism," as distinguished from 

 culture in vivo, i.e., "within the body"). Tissues can be isolated 

 from the body and grown in culture media in such a way as to 

 permit microscopic observation of individual cells under the 

 highest powers of the microscope during growth under controlled 

 conditions. Two biologists, the German botanist Haberlandt 

 and the American zoologist Harrison, independently made the 

 first experiments which led to the culturing of isolated tissues. 

 Haberlandt was the first to attempt to grow isolated cells and 

 tissues in culture, and Harrison the first to succeed in doing so. 

 Haberlandt was unsuccessful primarily because he used plant 

 material, but he pointed the way, as his words show: 



To my knowledge there have as yet been made no organized experi- 

 ments to cultivate isolated vegetative cells of higher plants in a suitable 

 medium; and yet the results of such culture experiments would throw 

 some light on those qualities and potentialities which the cell as an 

 elementary organism possesses. They should also reveal something of 

 the changing relations and mutual influences to which the cells, within 

 the many-celled organism as a whole, are exposed. 



