1886. ] BOTANICAL GAZETTE, 295 
on solid media, preferably on gelatine. My experience with the 
culture tube devised by Dr. D. E. Salmon has been entirely sat- 
isfactory. Its efficiency may be considered quite perfect. As it 
has been fully described! I need not dwell upon it here. The 
testing of liquid cultures is very simple and quickly accomplished. 
Either a minute portion is shaken up with liquified gelatine and 
the mixture poured on glass plates, or a platinum wire frequently 
dipped into the culture liquid is drawn several times across a layer 
of gelatine not yet congealed. In either case the developing col- 
onies will determine the purity or impurity of the liquid culture. 
I have almost invariably found the thirteenth or fourteenth gen- 
eration as pure as the first, and I should be surprised to find one 
out of every hundred impure. 
I will grant unreservedly that test tubes plugged with cotton 
wool are not fit for liquid cultures. For gelatine in such tubes, 
when frequently exposed, is invariably invaded after a time by 
fungi or bacteria. The plug being a nidus for dust, its removal 
is always attended with danger. Because a culture tube which 
eliminates the use of a large removable plug is more costly, it 
does not follow that it should not be used in scientific research. 
We know that in the department of physics, chemistry and phys- 
iology, the most advanced work is of necessity performed with the 
most complex apparatus. That there are those who do not suc- 
ceed in keeping liquid cultures pure, does not concern those who do. 
It behooves the former, in the interests of a true scientific spirit, to 
improve their apparatus and techinque instead of condemning the 
method. ver ee ae 
Conceding then for the present that cultivations in liquids 
can be kept free from contamination, the point at issue Is the em- 
ployment of liquids for diagnostic purposes. Whoever has paid 
any attention to the multiplication of bacteria in nutritive fluids, 
has no doubt been surprised at the variety of features which pre- 
sent themselves, and at the regularity with which the same ones 
appear in cultures of the same microbe. To illustrate how many 
different characters may be used in determining the kind of bac- 
teria and the purity of the cultivation, I will briefly outline a Ay 
of the more important ones as they have come under my own - 
servation, referring the reader to Miquel? for characters of bac- 
teria obtained from the air, soil and water. _ 
Every cultivation made in a tube shaped like a test-tube a9 
sents three regions for observation—the liquid itself, its surface, 
1 First Annual Rep. Bureau of Animal Industry, Dept. Agriculture, 1834, p. 229; Ameri- 
ean Monthly Microscopical Journal, 1884, p. 185. a es 
2 Annuaire de 1’ Observatoire de Montsouris pour l'an 1885, p. 577. 
