132 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
a spoon. In this will be found the diatom-frustules, supported by the 
air which they contain, and they have then simply to be separated by 
repeated filtering. 
Isolation of Rennet from Bacteria Cultures.* — Prof. H. W. Conn 
describes seven bacteria which possess the power of producing a rennet 
ferment in large quantities. F or the detailed description of the microbe 
the original should be consulted. The method of isolating the ferment 
is as follows : — “ The bacteria in question are cultivated in milk for 
several days, and in some cases for two weeks. By this time the curd 
is precipitated and at least partially dissolved, and the result is a some- 
what thick liquid containing of course immense numbers of bacteria. 
This liquid is filtered through a porcelain filter to remove the organisms, 
and a clear, usually amber coloured filtrate is thus obtained. The 
filtrate contains in solution all of the soluble chemical ferments which 
may have been formed by the bacteria. This filtrate is now acidified 
with H 2 S0 4 and then common salt added to a state of supersaturation. 
When this condition is reached there appears on the surface of the liquid 
a considerable quantity of snow-white scum. This scum is removed 
from the liquid, purified if necessary by precipitation, and then dried. 
It produces a snow-white powder, which upon experiment is found to be 
active in this curdling action upon milk, and to have all the essential 
characters of rennet. The ferment thus obtained is not chemically pure, 
containing, besides the rennet ferment, a varying amount of the tryptic 
ferment formed at the same time; but the rennet ferment is most 
abundant and very active. This ferment can be kept indefinitely, is 
killed by heat, acts best at a temperature of 30-35° C., and curdles 
sterilized milk under proper conditions in half an hour. Experiment 
shows that no organisms are present in the curdled milk, and there is 
thus no doubt left that we are dealing with a chemical ferment similar to 
rennet, and which is produced by the growth of these micro-organisms 
in milk. The ferment does not appear to be exactly identical with 
rennet, some of its chemical tests being different. This may be due to 
the impurities which are present or to an actual difference in the 
ferment.” 
Butter sack’s Vaccinia Microbe, t — Dr. A. Draer has examined pre- 
parations made from vaccine pustules, serum, blood, saliva, and egg 
albumen, for certain forms described by Buttersack as occurring on 
vaccinia pustule. In 64 per cent, of the preparations the Buttersack 
body was present, and the author comes to the same conclusion as Land- 
mann, viz. that these appearances are entirely artificial, and can be 
produced in any albuminous fluid by the method of preparation. 
The method was to treat cover-glass films for 15 minutes with a 7 per 
cent, nitrate of soda solution, and then for an equal length of time with 
5 per cent, sulphuric acid. The cover after having been washed for an 
hour was dried, placed on a slide, and examined. The cover was fixed 
by small bits of wax, and the medium through which the preparation 
was viewed was, of course, air. 
* Science, xx. (1892) p. 1892; and also Fifth .Report of the Storrs School of 
Agriculture, 1892, pp. 106-26. 
f Centialbl. f. Bakteriol. u. Parasitenk., xvi. (1894) pp. 561-4. 
