ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 453 



Micro-organisms in the Atmosphere.* — Dr. P. F. Frankland describes 

 a new method by means of which he claims that the estimation of organisms 

 in the air can be more accurately obtained, 



A known volume of air is aspirated through a glass tube containing two 

 sterile plugs, the first of which is more pervious than the other. The two 

 plugs are then transferred to two flasks, each containing melted sterile 

 gelatin-peptone, and plugged with sterile cotton wool. The plug is care- 

 fully agitated, and when it has become disintegrated and mixed with the 

 gelatin, the latter is congealed, so as to form an even film over the inner 

 surface of the flask. The flasks are incubated at a temperature of 22° C, and 

 after four or five days the colonies derived from the organisms contained in 

 the plug make their appearance. 



The process possesses all the advantages of a solid medium. The results 

 are not affected by aerial currents. The collection of an adequate quantity 

 of air takes but little time, so that a much larger volume can be examined 

 than by Hesse's method. The apparatus, being very simple, can be used 

 where there is no special laboratory. 



Distribution of Micro-organisms in the Air.f — Dr. P. F. Frankland 

 and Mr. T. G. Hart add to their previous experiments with Hesse's 

 apparatus on the prevalence of micro-organisms in the air. The number 

 (per 10 litres of air) varies greatly with the season, e. g. in January, 4, and 

 in August, 105 were found to be present. Experiments in crowded rooms 

 also show the enormous increase in number of micro-organisms ; thus in the 

 library of the Eoyal Society, during a conversazione, as many as 432 per 

 10 litres were found. By exposing dishes filled with nutrient gelatin, the 

 authors were able roughly to estimate the number of micro-organisms falling 

 on a given horizontal surface. 



Micro-organisms of the Soil.| — Herr B. Frank has examined the living 

 organisms found in various samples of soil taken from localities where 

 there seemed no possibility of their being influenced by human agency. 

 Among the forms found in most of the cultures, but not without exception, 

 were a Cephalosporium, a simple Botrytis-iovm., a Torula-fovm, an Oidium, 

 in one case a Mucor, and a Torula-tovm with nearly spherical bud-cells. 

 Invariably there was also present, in all the cultures, a Schizomycete, 

 presenting, in all the samples, a similar succession of forms of development. 

 About the second day it made its appearance as a LeptotJirix, causing the 

 gelatin to deliquesce. The threads collect into an interwoven mass, and 

 then break up into the second or Bacillus-foxm, which increase rapidly or 

 finally divide again by bipartition into the third or Bacterium-form of very 

 short rods or oval cells. Within the cells are formed shortly oval, strongly 

 refringent spores, usually one or two near the end of each rod ; and these 

 close the series of development. The rods become disorganized and their 

 membrane gelatinized, the spores becoming thus collected into zoogloea-like 

 masses, from which they again germinate in the form of rods. The different 

 forms may be motionless or may display various degrees of motility. The 

 bacilli are frequently curved in a comma-form. This universally distribiited 

 microbe of the soil Frank proposes to call, according to its stage of de- 

 velopment, Leptothrix terrigena, Bacillus terrigenus, or Bacterium terrigenum. 

 Its closest resemblances are with the hay-bacterium and anthrax. 



The best nutrient materials for this microbe of the soil are gelatin and 

 decoction of plums. Pure cultures exhibited no tendency to nitrification, 

 i. e. to the conversion of ammonia-salts into nitrites or nitrates ; and the 



* Proc. Eoy. Soc, xli. (1886) pp. 243-6. t Ibid., pp. 446-7. 



X Ber. Deutsch. Bot. Gesell., iv. (1886), Gen. Versamml., pp. cviii.-cxviii. 



