HOWARD: CARRIAGE OF DISEASE BY INSECTS 217 



measured by the immersion method, immediately after imbedding 

 in a liquid, appear to be a = 1.470, (3 and y = 1.515, but on 

 standing in an immersion medium the liquid slowly penetrates 

 the grains, probably displacing air and possibly some water, 

 and after remaining several days in the liquids and y of the 

 grains match a liquid with an index of refraction of 1.602, and 

 a, one with an index of 1.558. These are believed to be the in- 

 dices of refraction of the mineral. Loss of water, even to the 

 extent of 17 per cent, causes no appreciable change in the optical 

 properties, except a deepening of the color. 



A chemical analysis of the mineral is given and the loss of H 2 

 at different temperatures. This analysis and analyses of rector- 

 ite, leverrierite, batchelorite, kryptotile, and delanouite are 

 compared, and show some variation in the water content and, 

 more especially, in the Si0 2 : A1 2 3 ratio, which varies from 1.86 

 in batchelorite to 3.95 in delanouite. However, optical study 

 of the six minerals indicates that they belong to a single group, 

 probably related to the micas. Analyses of muscovite show 

 almost as wide a range in the Si0 2 : A1 2 3 ratio. The formula of 

 the leverrierite group may be written Al 2 3 .2 ± Si0 2 .2| ± H 2 0. 



MEDICAL ZOOLOGY. — The carriage of disease by insects.^ 

 L. 0. Howard, Bureau of Entomology. 



In his opening remarks the speaker called attention to the 

 fact that the whole great field of the carriage of disease by in- 

 sects has been developed within the last twenty years. He 

 showed that in the standard medical works of twenty years ago, 

 such as for example the 1895 edition of Osier's Principles and 

 Practice of Medicine, there occurs absolutely no mention of 

 insects in connection with tne etiology of disease, e'ther of man 

 or of the higher animals; yet at the same time he showed that as 

 early as 1889 Theobald Smith had discovered the causative 

 organism of the so-called Texas fever of cattle (Babesia bovis) 

 and that with the experimental aid of F. L. Kilbourne he had 



1 Address as retiring President of the Washington Academy of Sciences, de- 

 livered February 1, 1917. Abridged by the author. 



