The Organism and Its Cells 175 



when kept under proper conditions in microscopic prepara- 

 tions. And more recently Oppel, applying the new methods, 

 has described, figured, and discussed at length mitotic divi- 

 sions of cells isolated from various tissues of the cat. 



When we pass from the question of the independent life 

 of individual cells to that of the independence of organs, 

 or organized groups of cells, the prospect changes consider- 

 ably. Harrison, in one of his earliest publications, says: 

 "While the cell aggregates, which make uj) the different 

 organs and organ complexes of the embryo do not undergo 

 normal transformation in form, owing no doubt in part to 

 the abnormal conditions of mechanical tension . . . the in- 

 dividual tissue elements do differentiate characteristic- 

 ally." ^^ Without raising the question as to how "charac- 

 teristically" the individual elements can differentiate while 

 the cell aggregates "do not undergo normal transforma- 

 tion," the assertion that the aggregates do not transform 

 into organs is sufficient for the point being made. 



Carrel and Burrows have described "tubular formations" 

 in cultures of both the kidney and the thyroid gland of the 

 chick. The growth of kidney tubules is affirmed with special 

 particularity. The authors write : "At several points, tubu- 

 lar formations were observed which extended themselves a 

 considerable distance toward the middle of the plasma. Tlieir 

 ends were rounded, their lumina open, and their walls formed 

 of cells which had the appearance of epithelial cells. These 

 formations resembled renal tubules." ^^ 



The production of these structures is surely interestipg, 

 but more interesting is the question raised by the last sen- 

 tence: are the formations actually renal tubules, or do thcv 

 only resemble them.^ That no organization of cells into 

 normal organs takes place in these ^^cultures'^ is attested 

 by all who have pursued these investigations, so the state- 

 ment by Carrel and Burrows that the formations resemble 

 kidney tubules is to be taken as literally true, and to be 



