An extremely rare laryngeal hamartoma causing inspiratory stridor in a 6-week-old infant is reported and the histology discussed. The tumor is benign and responds to simple excision. No other cases have been found in the 20th century American literature.

A case of acute myelocytic leukemia (AML) occurring in the tonsillar fossa as an ulcerating lesion with a neck mass is described. Other common occurrences of AML in the upper respiratory tract are discussed. This disease entity may be confused with squamous cell carcinoma on initial examination.

To elucidate the process of contact inhibition in mammalian cells, we investigated the kinetics of growth arrest in [3H]thymidine labelled embryonic chinese hamster (Cricetulus griseus L.) cells after the addition of various concentrations of unlabelled cells. It was observed that after the contact inhibition concentration had been reached, the cells grew undisturbed for one more generation. In the following 24 hr the concentration fell back to the level at the beginning of the experiment and stayed there.

A chemostat in which mammalian cells can be raised in continuous suspension culture is described. It is constructed from commercially available parts. This apparatus has the advantage over earlier models in that the medium can be pumped off free of cells, thus suddenly increasing the cell concentration in the culture. The apparatus has been successfully used in studies on contact inhibition.

SUMMARY A simple automatic counting device for cells on Petri dishes is described. The device is tested up to 1 × 104 cells (0·01 m)−2 and counts linearly without coincidence error. The counting time for each dish is c. 3– 4 min including the time required to place the dish in the apparatus.