McCutcheon index

The McCutcheon index or chemotactic ratio is the ratio of the net displacement of a bacterium to the length of its actual path.^[1][2]

$\text{McCutcheon index}= {\text{Displacement}\over \text{Distance}}.$

It is named after Morton McCutcheon who introduced it to describe chemotaxis in leukocytes.

References

1. Chemotaxis in Leukocytes
2. The response of human neutrophils to a chemotactic tripeptide