48 



SCIENCE 



[N. S. Vol. XLVII. No. 1202 



(6) Percentage. The same thing may be 

 done from the percentage column above, i. e., 

 5 per cent, of the .01 c.c. and 5 per cent, of 

 the .1 c.c. tubes revert to make the 90 per 

 cent, of the 1 c.c. tubes up to 100 per cent., 

 leaving 35 per cent, of the .1 c.c. tubes posi- 

 tive as before. 



Single Dilution Method. — Frequently deter- 

 m.inations are made in one dilution only. In 

 this ease the " Percentage Positive " gives the 

 " Score " as where several are used. 



Split Dilutions. — ^Where other " Dilutions " 

 are used than the regular ones, the same 

 methods can be applied by using the corre- 

 sponding "Dilution" in the computation. 



CONCLUSION ARGUMENT 



The reason the above simple methods give 

 the " Geometrical Mean " arises from the fact 

 that the ordinary bacteriological dilution scale 

 is in reality a logarithmic scale, and the 'aver- 

 age dilution is the average logarithm or the 

 logarithm of the " Geometrical Mean." A 

 vast amount of published bacteriological data 

 to be considered at some other time proves 

 that bacteriological results follow a logarithmic 

 probability curve, from which it follows that 

 the median value closely corresponds to the 

 geometrical mean. It is equally probable, 

 therefore that another sample would be 

 greater as less than the geometrical mean. 

 There is nothing in this principle to limit the 

 application of the method, and by intelligent 

 application it can be employed in interpreting 

 all similar forms of data. 



WiLLUM Firth Wells 



riELD LABOEATOEY, 



MiLPOED, Conn. 



PITTSBURGH MEETING OF THE AMER- 

 ICAN ASSOCIATION FOR THE AD- 

 VANCEMENT OF SCIENCE 



The seventieth meeting of the American Asso- 

 ciation for the Advancement of Science was held 

 in Pittsburgh, Pennsylvania, on December 28, 

 1917, to January 3, 1918. It seems to be a very 

 general opinion of the members who attended that 

 the meeting was practically an unqualified success. 

 The total registration at the office of the perma- 

 nent secretary was 692. 



It is impossible to estimate the number of mem- 

 bers who were deterred from attendance by the 

 statement sent to the press by the Pennsylvania 

 Railroad late in December, and by the published 

 letter of Dr. Richards, but it is obvious that no 

 congestion of traffic, and no clogging of trains re- 

 sulted from the meeting. Of the 692 persons reg- 

 istered, 194 came from Pittsburgh and other parts 

 of Pennsylvania, 122 registering from Pittsburgh 

 alone. The remaining attendance came as usual 

 from all points of the compass, and were distri- 

 buted on the regular trains arriving at different 

 times, so that their train presence was scarcely to 

 be noticed. 



The attendance was distributed as follows: from 

 Pittsburgh and the rest of Pennsylvania, as just 

 stated, 194, New York 84, Ohio 59, District of Co- 

 lumbia 44, Illinois 34, Massachusetts 26, West 

 Virginia 21, Indiana 20, Michigan 18, Wisconsin 

 15, Maryland, Missouri and Canada 14 each, Iowa 

 and Texas 13 each, New Jersey and Virginia 11 

 each, California 10, North Carolina 8, Connecticut, 

 Tennessee and Kansas 6 each, Minnesota and Ari- 

 zona 5 each. New Hampshire, Louisiana and Mon- 

 tana 4 each, Maine, Delaware and Kentucky 3 

 each, Japan, Nebraska, Utah, Oregon and Colorado 

 2 each, Rhode Island, Georgia, North Dakota, 

 Arkansas and Wyoming 1 each. 



The interest of the meeting was enhanced by 

 the presence of the following foreigners, who were 

 made honorary associates for the meeting: Lieu- 

 tenant Georgia Abbetti, of the Italian Military 

 Commission; Lieutenant G. P. Thompson, of the 

 Eoyal Plying Corps of Great Britain; Captain De- 

 Guiche, of the French Military Commission, and 

 Dr. Shigetaro Kawasaki, chief geologist of Korea. 

 The impressive keynote of the whole meeting was 

 war preparation and efficiency. This was borne out 

 not only in a number of symposia devoted to spe- 

 cific war topics, but also in other discussions, and 

 in other papers, the titles of which would not 

 necessarily lead one to expect a development along 

 the line of war preparation. The local press was 

 keen in noticing this aspect of the meeting, and 

 paid great attention to the papers of the entire 

 session. 



The opening general session of the association 

 was held Friday night, December 28, in the lecture 

 hall of the Carnegie Institution. The president of 

 the Association, Professor Theodore W. Richards, 

 of Harvard University, was absent, and Dr. George 

 H. Perkins, of the University of Vermont, senior 

 vice-president, presided. Mr. H. M. Irons, city at- 



