TISSUE CULTURE 



347 



TISSUE CULTURE 



of culture, however, must at the present 

 time be considered as merely a step in 

 the development of other and still 

 more useful culture types. Klein 

 (Klein, G., Cancer, 1950, 3, 1052) and 

 others have been able to grow numerous 

 types of malignant tumors intraperi- 

 toneally in animals, and by repeated 

 subinoculation in this site have caused 

 the tumor cells to form a dense cell sus- 

 pension in the ascitic fluid of the animal. 

 It appears quite probable that with 

 further increase of our knowledge of 

 the factors which control the prolifera- 

 tion of cells on these various types of 

 substrates, it may be practical to en- 

 tirely eliminate the necessity of the 

 substrate, as we now know it. By 

 control of culture conditions it may be 

 possible to routinely grow many types 

 of cells free-floating, or virtually free 

 floating, as a suspension in a nutrient 

 fluid. Already these possibilities are 

 being explored. 



Numerous other types of tissue cul- 

 ture preparations are employed for 

 special purposes. A watchglass culture 

 is often used in embrvological studies 

 (Fell, H. B., above cfted). Porter, K. 

 R., Claude, A. and Fullam, E. F., (J. 

 Exp. Med., 1945, 81, 233) have intro- 

 duced a special flask, for use in a roller- 

 tube unit, designed particularly for 

 electron microscopy. Special flasks 

 designated T-12 and T-60 flasks (Earle, 

 W. R. and Highhouse, F., unpublished) 

 have been designed to handle quan- 

 titatively cultures planted from cell 

 suspensions obtained from cellophane 

 substrate cultures. These will be con- 

 sidered in more detail below. 



3. The Cells in Cultures. With respect 

 to the types of cells which may he grown 

 in tissue culture at the present time, 

 certain rough but possibly useful gener- 

 alizations may be made. 1. Nearly 

 any type of cell can be kept alive or in 

 a state of survival, from a few hours 

 to a few days. 2. Cell proliferation is 

 probably not to be expected at all of 

 anatomically incomplete cells, such as 

 the erythrocyte, which lacks a nucleus. 



3. Embryonic cells which have not 

 yet assumed a high degree of func- 

 tional specialization or differentiation, 

 are in general easier to grow than adult, 

 highly specialized or differentiated cells. 



4. Manj' malignant cells are more 

 easily grown than are the normal cells 

 from which they arise. For instance, 

 there has been no satisfactory long- 

 term culture of the normal mammary 

 gland epithelium, although there have 

 been frequent instances of culture of 

 epithelium from carcinoma of the mam- 

 mary gland. 5. That group of cells 



which we loosely designate as "fibro- 

 blasts", and closely related cells which 

 arise from the mesenchyme or meso- 

 derm are in general reasonably easy to 

 grow, particularly from very young 

 animals. The epithelial tissues, how- 

 ever, especially the highly differen- 

 tiated secretory epithelia, from the 

 liver or the thyroid, are often far more 

 difficult. 6. It appears quite probable 

 that as our knowledge of the nutrition 

 and endocrine control of specific cell 

 types increases we shall become in- 

 creasingly able to grow these more 

 highly specialized cells. 7. At present 

 relatively few cell strains, normal or 

 malignant, have been maintained in a 

 state of rapid proliferation for as long 

 as one year. 9. If an easilj' grown cell 

 type can be used with equal value 

 to one which has never been satisfac- 

 torily grown, the easily grown cell is 

 obviously the one of choice. The study 

 necessary to grow luxuriantly a cell 

 type which has never been grown may 

 well take years. Any problem which 

 depends for its success on cultivation 

 of a cell type which has never been 

 satisfactorily grown should be entered 

 into with caution and only after a careful 

 evaluation of whether the results to be 

 obtained justify the expenditure of 

 effort involved. 



Until recently it has never been pos- 

 sible to grow a single isolated tissue 

 cell of any type. Consequently it has 

 never been possible to establish a pure 

 culture or strain of cells which could be 

 considered with assurance as made up 

 of only one single cell type. Cultures 

 of such cells as the chick-heart fibro- 

 blasts or the malignant mammary epi- 

 thelium have in instances been cultured 

 and have appeared stabilized for ex- 

 tended periods of years; but there has 

 been no assurance that all cells within 

 such cultures were identical in type or 

 in origin. At best they could be con- 

 sidered as made up of similarly ap- 

 pearing, or comparably reacting cells, 

 as judged by the tests used. Recently, 

 however, methods have been worked 

 out by which a single isolated cell 

 from the subcutaneous connective tis- 

 sue of a CsH strain mouse was success- 

 fully isolated and grown (Sanford, K. 

 K., Earle, W. R. and Likely, G. D., 

 J. Nat. Cancer Inst., 1948, 9, 229). 

 This cell strain has continued to pro- 

 liferate luxuriantly'- in horse serum and 

 chick embryo extract for a number of 

 years. (The strain has now been made 

 available to laboratories having facili- 

 ties for carrying it.) The methods used 

 have allowed proliferation of a number 

 of other types of isolated cells both 



