Adaptation of an automatic bacterial colony counter proved to be an efficient procedure for detecting and quantitating tumor growth in mouse lungs prepared by the Wexler method of India ink insufflation. After correlation of the size discriminator settings on the automatic counter with the Wexler visual scale, the amount of tumor growth in the lungs of 52 mice was determined by eye and independently by the automatic counter. There was no statistical difference between the two procedures.

When the mouse lungs were grouped according to the number of tumors computed by eye, there was no statistical difference between the two counting procedures in any of the groups. The standard deviation was independent of the number of tumors in the lungs. This caused the precision of the automatic counter to be poor in lungs with few tumors because the error was a greater percentage of the total. In lungs with a large number of tumors, which were difficult to count by eye, close agreement between the two methods of counting was demonstrated.

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