THE RELATION OF CELLS TO ONE ANOTHER 215 



cinoma sends forth into the medium buds and sinuous 

 branches composed of densely packed cells and grows 

 to resemble an alveolar carcinoma, without any connective 

 tissue to fill the spaces between the alveoh. Thyroid cells 

 may also form alveoH in which secretory substance is 

 observed. Evidently, therefore, cells isolated from the body 

 show a bhnd tendency to form organs even when there is no 

 organism and no object for such formation. This purposeless 

 organization is clearly the expression of certain fundamental 

 properties of the cells. Blood monocytes, on the contrary, 

 never congregate as a tissue. When they are cultivated in a 

 flask, they scatter all over the coagulum. It is only when 

 they have reached its edges that they begin to grow in a 

 denser formation. But the cells never come in contact on 

 their sides. Sometimes they unite in a chain, but it is never 

 a constant and definitive structure. If compelled to aggre- 

 gate in a mass, they generally die. Their scattering through 

 the body is the expression of an elementary property and 

 not of an impulse to protect the organism against the invasion 

 of bacteria or the accumulation of dead cells or foreign 

 bodies. 



7. Production by the Cells Themselves of Certain Conditions 

 of their Environment. It is very probable that the fluids of 

 the body, such as interstitial lymph and blood serum, are 

 entirely the result of cell activity. But the mechanisms 

 governing the formation of interstitial lymph by the tissues, 

 and the eff'ect of the lymph on the tissues are still unknown. 

 Nevertheless, it has become possible to investigate the 

 manner in which groups of cells may modify their immediate 

 environment. When a fragment of pure culture of fibroblasts 

 is placed in a coagulum stained with phenol red, it quickly 

 surrounds itself with an orange-yellow crown, and a piece 

 of spleen creates for itself a still more acid atmosphere. 

 Colonies of blood monocytes do not produce any local change 

 in the color of the medium, but they progressively modify 

 the hydrogen ion concentration of the entire coagulum. 

 When fragments of spleen are being transformed into 

 sarcoma by Rous virus, the production of acid becomes more 

 active. In composite tissues made of normal and sarcomatous 

 fibroblasts living in symbiosis, golden-yellow spots^on an 



