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TEN TEXT FIGURES AND OXE PLATE (SIX FIGURES) ISTRODUCTLONThe purpose of this study is to investigate cytological changes in the rat thyroid under corditions of experimental stimulation arid depression. It will be shown that when one compares a series of activated glands with the normal, he can trace the progressive mobilization of certain intra-cellular organoids which probably act collectively to form secretion products. I n the same manner, depression in activity of the gland also causes certain noticeable rnicroscopic changes.These appear to result from the sudden decrease in secretory activity. The heat depressed glands can be readily compared cytologically with those which have been stimulated to activity. By this method, one can obtain at least a partial picture of the intra-cellular changes which accompany secretion production.Progressive exposures to heat and cold were used to bring about the desired changes in secretory activity. This method was chosen because animals are forced to react to these stimuli in their natural environment, and have thus built up some physiological response to these conditions. For this reason, the reaction is not essentially foreign to them, and should be similar to that found under normal conditions.

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REACTION OF RAT OMENTUM TO PARTICULATE MATTER 409apparently gave some immunity in the vaccinated group at institution Y, but none at X. V-2 produced a slightly, but perhaps not significantly, greater antibody-response than did V-1 , as judged by complement-fixation and neutralization-tests. It is quite probable that subclinical infections accounted for some of the increase in antibodies. It also appeared that the response in complement-fixing antibodies produced by the two vaccines was considerably less in degree than the response following infection. Swnzmary. Studies were conducted at two large institutions during an outbreak of influenza A which was proven by complementfixation tests. Persons at both institutions received a living virus and complex forrnalinized vaccine previous to the outbreak. An epidemiological survey revealed some protection at one institution, but none at the other. There was no obvious difference in the prophylactic efficacy of the two vaccines in the relatively small group of 829 individuals studied.