In our previous studies (1, 2) concerning tissue specificity we were constantly faced with the fact that the various tissues showed a very great complexity of relationship. In many cases this complexity tended to cloak the evidence of the tissue specificity and it was only by means of comparative, quantitative studies that we were able to prove certain facts. It was, however, evident that tissue specificity could actually be demonstrated in the case of the tissues which were used (namely, liver, kidney, spleen, brain, muscle and testicle). Furthermore, there was noted a relationship between the various organs of animals of the same species, which was evidently due to a species specificity. In addition there were suggestions of a further relationship between the various organs which could not be explained by the simple species specificity.