As to the influences of temperature and humidity upon the transition of larva to imago he finds that if humidity diminishes, a smaller number of larvæ reach the adult stage; and also that a saturated humidity (in artificial cultures), causing condensation of water in the substratum, is very fatal to larvæ. He offers the thought that this, perhaps, explains why only small numbers of fleas are found on field rats which live in holes in rice fields which are necessarily damp, especially in the rainy season. His experiments to determine the duration of life of fasting fleas were made with laboratory-bred fleas which had never fed on blood and with fleas which had already sucked blood. The duration of life was variable, but of those fleas already fed with blood three-quarters (¾) perished within 10 days and the remainder lived from ten to twenty days, only one-tenth, however, surviving for 13 days, if moist conditions were maintained. High temperature was determined to be an unfavorable condition. If from these findings one should attempt to predicate or predict the extension of plague in house rats--based on flea prevalence--and this with relation to climatic conditions, we should be led to the conclusion that the rainy season, with its greater humidity, would be quite the most favorable time of year for rat plague extension in Manila and, upon the contrary, that the hot dry season through its unfavorable influence upon flea breeding would be the least favorable season for rat plague in Manila. The hot months of 1913 did not bear out this reasoning, however, for during these months rat plague was at its height. That increased prevalence of human plague has not gone hand in hand with increased prevalence of rat plague in Manila, may be explained, I feel sure, by the activity of our efforts to destroy rats and to remove the people from close relationship with them. Another factor of possible explanation of the greatest prevalence of human plague in Manila during the late rainy season of 1912 (October), is the fact that rats are certainly driven above ground into houses and therefore into closer relationship with man by heavy rainfall and the consequent flooding of their subterranean homes. It appears, therefore, that the seasonal explanation of greater plague prevalence, rat or human, is susceptible of several interpretations and I feel sure that in countries like the Philippines seasonal variations in heat do not suffice to rid the rats of fleas during any months of the year. If, then, conditions of rainfall serve to drive the rats above ground and indoors during certain months, it would be reasonable to expect more human plague from closer relationship of rat and man,--provided that no special measures were carried out. Such, however, is not invariably the rule, if statistical studies are to be taken as evidence, and so we are reminded that generalizations for countries of different climates and seasons are not wholly reliable.