ABSTRACT
A method is described by which cells in the zone of outgrowth of cultures in flasks can be photographed at definite intervals over long periods of time.
The rate of growth of chick heart tissue when growing in the presence and absence of embryo extract has been investigated.
A numerical value, the growth index, has been calculated which expresses the mitotic activity of the culture during the periods of observation. In plasma alone the growth index is approximately 3 after 20 hours of growth and falls to zero at the 70th hour if the fluid medium above the plasma (in this case Tyrode) is not renewed. In plasma and embryo extract-(fluid medium embryo extract unchanged) the growth index is approximately 9 after 30 hours of growth, and falls to zero at about the 140th hour. If the fluid medium is frequently renewed with fresh embryo extract the growth index quickly falls to 3, and in the one case followed for more than 4 days it remained fluctuating about that level for the next 6 days, in fact for as long as it was practically possible to prolong the experiment.
It is suggested that the method has many applications in connection with problems associated with the growth rates of tissues and organisms.
