242 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
directly on tlie organism ; and it is extremely desirable that experiments 
should be made on tbe action of light on living cells of animals, as 
the results obtained would probably be of importance as regards sun- 
burn, sun-baths, and other matters. 
Acetic Acid Bacteria.*— Prof. E. C. Hansen finds that acetic acid 
bacteria occur under three chief forms — chains, filaments, and swollen 
forms Cultivated on a suitable medium at 34° C. the vegetation 
consists of chains; if this be cultivated at 40J° it is replaced by 
filaments Under these conditions filaments 200 fx and more long are 
developed from individuals measuring only 2-3 fx. Transferred to 34° 
the long filaments are reduced to the chain form again. If the develop- 
ment from 34°-404° be followed step by step, it will be found that the 
organism, or rather its elements, increases not only in length but in 
thickness, "and often to such a degree that striking swellings or dilata- 
tions are apparent. So different are the three forms, that they would be 
assuredly taken for three distinct species if observation had not proved 
them to have arisen one from the other. 
Gaseous Products of Bacteria. - ]* — The researches of Dr. W. Hesse on 
the gaseous metabolic products of bacteria, and especially on their rela- 
tion to oxygen and carbonic acid, have led him to conclude that bacteria 
respire just like animals. For his experiments the author used Hempel’s 
apparatus and the following organisms : — the bacilli of cholera, anthrax, 
typhoid, glanders, tubercle, and Pfeiffer’s capsule bacillus, as well as 
the three anaerobes, symptomatic anthrax, tetanus, and malignant oedema. 
The results may be summed up very shortly. Bacteria take in oxygen 
and give off carbonic acid ; the more freely they grow the more copiously 
they do so. Under exactly similar circumstances the interchange of 
gases will be exactly the same. Therefore the oxygen present in the 
cultivation vessel will be used up at a rate different for different 
organisms, and varying with difference in the environment, e. g. the 
medium, the temperature, &c. The quantity of the oxygen used up and 
that of the carbonic acid produced are therefore different for different 
bacteria and under different conditions of environment. This quantity 
can be measured. And if the quantity of oxygen lost or of carbonic 
acid gained can be practically estimated, this quantity might become 
a factor for differential diagnosis or for determining the age of a culti- 
vation. 
Respiration-Figures of Mobile Bacteria.:}: — By respiration figures, 
Dr. M. W. Beyerinck means the arrangement assumed by mobile 
microbes under the influence of oxygen and nutritive media. 
The figures were studied under two conditions, in test-tubes and as 
wedge-shaped layers between a slide and cover-glass. In the first case 
a test-tube is nearly filled with water, and a bean ( Phaseolus vulgaris 
var. nanus ) dropped in. In a day or two bacteria will be found forming 
a- cloudy band across the tube at some distance between the bean and 
the water surface. This band is called the bacterial level. Levels 
* Ber. Deutsch. Bot. Gesell., xi. (1893) Gen.-Versammluugs-Heft, pp. 69-73. 
t Zeitschr. f. Hygiene u. Infektionskrank., xv. (1893) No. 1. See Centralbl. f. 
Bakteriol. u. Parasitenk., xiv. (1893) p. 730. 
X Centralbl. f. Bakteriol. u. Parasitenk., xiv. (1893) pp. 827-45 (1 pi., 12 figs.). 
