256 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The smallest number during any month was 17 in February; the 

 largest, 197 in October. 



Similar tables are given of the number of germs in the air in 

 Paris. February is still the lowest month, but the highest are June 

 and July ; and the average number is nearly ten times as large as 

 at Montsouris. Of these bacteria, 93 per cent, were micrococcus, 

 5 per cent, bacillus, and 2 per cent, bacterium. In hospitals the 

 number of germs is very much larger still; amounting, even during 

 the summer months, to an average of 5600 per cubic metre, and in 

 the autumn to considerably over 10,000. M. Miquel considers the 

 air of hospitals to be a very large source of infection for contagious 

 diseases, such as small-pox, scarlet fever, diphtheria, erysipelas, 

 typhus, &c. 



An examination of the bacteria in the soil showed at Montsouris an 

 average of 750,000 ; in the Eue de Eennes, 1,300,000 ; in the Eue 

 Monge, 2,100,000 germs per gramme. 



A curve representing the number of bacteria present in the air very 

 nearly corresponds with a curve of the weekly mortality of Paris, 

 published under the authority of M. de Bertillon in the ' Bulletin de 

 Statistique Municipale.' 



The presence of ammoniacal (urine) ferments in the air is also 

 discussed. These he shows to be of three kinds, Micrococcus iirece, 

 Bacillus urecp, and Torula urece. Of the first he found 71, of the 

 second 19, of the third 10 per cent. 



Bacterium photometricum.* — T. W. Engelmann has further 

 investigated the remarkable properties of the bacterium sensitive to 

 light discovered by him,t which he finds in great quantities in the 

 branch of the Rhine at Utrecht in company with amoebas, Lecythiiim 

 hi/alinum, Polytoma uvella, Oxytriclia micans, and Anguillula. He con- 

 siders it an admirable test for the diathermancy of any medium for 

 the invisible ultra-red rays of the spectrum. 



A local accumulation of the bacterium was caused in a drop with 

 the assistance of the microspectral objective, with as wide and 

 intensely illumined a slit as possible. By gradually narrowing the 

 slit the characteristic accumulation of the bacterium in the ultra-red 

 between wave-lengths • 8 and • 9 /x was brought about ; and it was 

 ascertained how much the slit could be narrowed without entirely 

 dispersing the bacteria. The slit was now slightly widened, and as 

 soon as the quantity of bacteria in the inner ultra-red had increased, 

 the medium to be tested was inserted between the source of light 

 (heliostat or gas-flame) and the mirror of the microspectral objective, 

 and the slit again narrowed to the greatest possible extent consistent 

 with a considerable accumulation of the bacteria in the ultra-red. 

 In other cases, after the first determination, the slit was widened to 

 its utmost extent, and, after insertion of the medium, again narrowed 

 to the minimum. In others again, commencing with a closed slit, the 

 smallest opening was ascertained with which within a definite time 



* Pfluger's Arch. f. Physiol., xxx. (1882) pp. 94-128 (1 pi.), 

 t Cf. this Journal, ii. (1882) pp. 656 and 661. 



