Tissue correlations in linear samples

A line sample is made through an aggregate of many tissue types. The question treated is whether the observed distribution of heterotype contacts is consistent with a random placement of the tissues. A generating function in the form of a weighted Markov chain is set up and analyzed for various assumptions as to a priori probabilities. The case in which all tissue types but the pair being assayed are combined in a communal tissue is solved explicitly in the limit of a large sample. Corrections due to finite sample size and to the detailed structure of the communal tissue are carried out.