158 BACTERIA IN RELATION TO PLANT DISEASES. 
Lewton-Brain and Deerr have published a figure strikingly similar to Kern’s figure 
here listed as 39 (The Bacterial Flora of Hawaiian Sugars, Bull. 9, Exp. Sta., H. S. Pl. Asso. 
. Honolulu, 1909, p. 21, fig. 17). This was drawn from their Bacillus D, a sugar destroying 
species. Is is called by them a curious bipolar effect produced by carbol fuchsin staining. 
[This] consists of a faintly stained central part, with a very brightly stained circular body at 
each end. * * * It seems possible that the central body represents the spore, the two brightly stain- 
ing bodies the degenerated protoplasm of the remainder of the cell, while the walls of the cells have 
swollen up and become confluent with those of other cells lying close at hand. ‘This peculiar effect 
was not met with in the other bacteria stained in the same way, and was always obtained with D, 
so that it would appear to have some diagnostic value. 
Beyerinck devoted a paper to this subject in 1889. 
Kefir is composed of a yeast and a schizomycete in symbiotic relationship, the result of their 
combined action on milk being alcohol, carbon dioxide and lactic acid. He distinguished the yeast 
as a new form, Saccharomyces kefyr and described the schizomycete as Bacillus caucasicus. ‘These to- 
gether produce small plates which grow by the formation of local excrescences that increase in size 
and fuse at their base. In sour milk the kefir grains remain alive for a long time. He figures the 
yeast as occurring in a uniform thin layer on the outside of the grains. He also states in the text 
that the yeast occurs almost exclusively on the surface of the grains, the bulk of the mass being bac- 
teria. In some instances, however, he states that he saw chains or layers of the yeast in the interior 
of the mass. In the bacterial mass Beyerinck distinguished a cortical layer, and a so-called pith, 
with a central cavity partly or fully occupied by zoogloez masses. ; 
The yeast is oval. The measurements given by Beyerinck are 3 to 6u. It is easy to cultivate. 
It is able to convert milk-sugar into alcohol and carbon dioxide. After a long time it liquefies neutral 
or feebly alkaline lactose gelatin. This yeast tolerates a large amount of lactic acid (up to one-half 
normal), acetic acid on the contrary is very injurious to it. 
The yeast is said to invert milk-sugar by means of an enzyme, lactase. That the inversion pre- 
cedes the formation of alcohol was shown by the use of poured plates containing fish bouillon, 3 per 
cent sea-salt, and 7 per cent gelatin, to which was added some milk-sugar and then sown with his 
Photobacterium phosphorescens. After 2 days the gelatin became luminous. Later, as the food was 
exhausted the luminosity diminished, this organism being unable to use the milk-sugar present in 
the gelatin. If then the kefir yeast was placed on portions of the plate these portions again became 
luminous, indicating the liberation by the yeast of simpler, assimilable sugars from the milk-sugar. 
The bacillus produces lactic acid. It is mixed with other bacteria which are to be regarded as 
impurities. Some of these impurities are readily distinguished, 7.e., the bacilli producing carbon 
dioxide and hydrogen, or lactic acid milk ferments in the form of diplococci, Oidiwm lactis, and foreign 
yeasts. Other rod-shaped bacteria are less easily distinguishable, such as those producing acetic 
acid or lactic acid. The advantage of the symbiosis to the yeast is freedom from acetic acid and 
from putrefactive bacteria, which are assured to it by the presence of the lactic acid ferment. The 
advantages to the bacteria from the presence of the yeast are less clearly evident, but are believed 
by Beyerinck certainly to exist. He offers some hypotheses, but no actual facts. 
A good culture medium for Bacillus caucasicus is gelatin with serum of milk either neutral or 
feebly acidified with lactic acid. When such a medium is sown with water in which a fragment of 
kefir has been crushed, there appear after two or three weeks, between the yeast colonies, very 
minute and extremely slow-growing colonies of this lactic ferment. The most favorable temperature 
for the growth of these minute colonies is said to be 45° C., and then, of course, agar plates must be 
used. Bacillus caucasicus does not liquefy gelatin. It forms neither lactase nor invertase, but trans- 
forms milk-sugar, cane-sugar, maltose and glucose directly into lactic acid. The optimum tempera- 
ture for this change is 40° to 45°C. here is no special action on starch or casein. The fermentation 
and formation of lactic acid take place equally well in the presence or absence of free oxygen. 
“Under all conditions the ferment keeps the form of rods or filaments, which often remain 
united into chains and may become very long. I have never observed the least indication of spore 
formation, nor of motility.” 
Beyerinck was not able to obtain the kefir synthesis by using a mixture of the yeast and lactic 
ferment on lactose gelatin. 
In 1891, Mix published a contribution upon an American kefir. The work was done 
at Harvard University on material obtained from two different sources, 7. e., New Jersey 
and Ontario. Both specimens were lobed and fissured and of a. dirty brown color resemb- 
