ABSTRACT
In the foregoing paper (Bullough, 1949b) a doubt is expressed concerning the value of colchicine for collecting in the metaphase all those mitoses which normally occur during a 12 hr. period. It is probably true to say that most studies of animal mitosis made with the help of colchicine have been planned on two assumptions, namely that, within reasonable limits, the drug arrests every mitosis reaching the metaphase, and, equally important, that it neither increases nor decreases the number of resting cells entering mitosis. Following the pioneer work of Dustin (1934), Lits (1934) and others, these reasonable limits have been defined (see Allen, 1937) as a dose of 0·1 mg. given subcutaneously in water or normal saline and allowed to act for a period of 
hr. With smaller doses only a partial stoppage of mitosis is achieved; with larger doses the resting cells are prevented from entering the prophase; and with longer periods the number of arrested mitoses does not increase because there is a complete stoppage of all cell division.
