36 
PEOFESSOE TYNDALL ON THE OPTICAL DEPOETMENT OF THE 
of life. This augmented my perplexity. A third tube also showed scanty traces of life. 
I reverted to the second tube, where life had been so copious, and found that in it the 
organisms had become as scanty as in the others. I confined myself for a time to the 
three tubes of the first row of the six, going over them again and again ; sometimes 
finding a Bacterium here and there, but sometimes finding nothing. The first extra- 
ordinary exhibition of life it was found impossible to restore. Doubtful of my skill as 
a microscopist I took specimens from the three tubes and sent them to Prof. Huxley, 
with a request that he would be good enough to examine them. 
On the 22nd the search was extended to the whole of the tubes. Early in the day 
lively Bacteria were found in one of them ; later on, not one of the six yielded to 
my closest scrutiny any trace of life. On the evening of the 22nd a note was received 
from Prof. Huxley stating that a careful examination of the specimens sent to him 
revealed no living thing. 
Pipettes had been employed to remove the infusion from the test-tubes. They were 
short pieces of narrow glass tubing, drawn out to a point, with a few inches of india- 
rubber tubing attached to them. This was found convenient for bending so as to reach 
the bottom of the test-tubes. Suspicion fell upon this india-rubber. It was washed, the 
washing-water was examined, but no life was found. Distilled water had been used to 
cleanse the pipettes, and on the morning of the 23rd I entered the laboratory intending to 
examine it. Before dipping the pipette into the water I inspected its point. The tiniest 
drop had remained in it by capillary attraction from the preceding day. This was blown 
on to a slide, covered, and placed under the microscope. An astonishing exhibition of life 
was my reward. Thus on the scent, I looked through my pipettes, and found two more 
with the smallest residual drops at the ends ; both of them yielded a field rampant with 
life. The Bacteria darted in straight lines to and fro, bending right and left along the 
line of motion, wriggling, rotating longitudinally, and spinning round a vertical trans- 
verse axis. Monads also galloped and quivered through the field. From one of these 
tiny specks of liquid was obtained an exhibition of life not to be distinguished from that 
which had astonished me on the 21st. 
Obviously the phenomenon then observed was due to the employment of an unclean 
pipette. Equally obvious is it that in inquiries of this nature the experimenter is beset 
with danger, the grossest errors being possible when there is the least lack of care. 
♦ The door of this case had been opened with a view to testing the capacity of the 
infusions within it to develop and maintain life. For four weeks they had remained 
'perfectly clear. Two days after the door was opened and the common laboratory air 
admitted all six tubes were turbid, and swarming with Bacteria. Some of them were 
very long, and their wriggling and darting hither and thither very impressive. 
The chamber here referred to was again thoroughly cleaned, sealed, and permitted 
to remain quiet until its floating matter had subsided. On the 17th of November a 
fresh infusion of turnip was introduced into it through the pipette, boiled in an oil-bath, 
and again abandoned to the air of the case. 
