458 
DR. W. ROBERTS ON BIOGENESIS. 
juices and tissues of animals and plants are capable of producing organisms without 
infection by extraneous germs. In the third section the facts adduced in the two 
previous sections are considered in their bearing on the origin of Bacteria and Torulce , 
and some of the alleged cases of abiogenesis are tested experimentally. 
The experiments were all contrived on a plan which favoured not only the birth but 
the continuous growth of any organisms which made their appearance. The materials 
were both maintained at a suitable temperature and furnished with a free supply of 
air, so that the changes initiated might have an opportunity of going on until their 
nature became undoubted. 
In judging of the absence or presence of organisms, the microscope was, of course, the 
principal test. The magnifying-power generally employed was 500 diameters, controlled 
sometimes by a magnifying-power of 1200 diameters. In addition to this, however, 
note was always taken of the naked-eye appearances, of the presence or absence of 
turbidity, of a film on the surface, and of a deposit at the bottom, as well as of the 
reaction and odour. Signs of growth and multiplication were regarded as the only 
indefeasible evidence of living organisms. 
The term Bacteria is used in the comprehensive sense adopted by Cohn to include 
the various organisms described as vibrios, micrococci, microzymes, and schistomycetes. 
The terms Torulce and fungoid vegetations are used to designate organisms belonging to 
the type of the yeast-plant and the Penidlium glaucum. The word germ is used 
simply in the general sense of a particle endowed with the power of provoking germina- 
tion in a suitable medium. 
Section I.— ON THE STERILIZATION BY HEAT OE ORGANIC LIQUIDS AND MIXTURES. 
When beef-tea or a decoction of turnip is boiled for a few minutes in a flask, of which 
the neck is plugged with cotton-wool, the liquid passes into a state of permanent sterility. 
It can be kept for months and even years exposed to the most favourable conditions of 
warmth and light, with a constantly renewed supply of air ; but so long as the cotton- 
wool plug remains undisturbed, neither Bacteria nor Torulce , nor any other organisms, 
make their appearance in it. The liquid has not, however, lost its fitness to nourish and 
promote the growth of these organisms ; for if the cotton-wool plug be withdrawn so as 
to admit unfiltered air into the flask, or if a drop of ordinary water be introduced, 
Bacteria or Torulce speedily make their appearance, and grow and multiply with the 
utmost luxuriance. 
This experiment, which will be referred to as the “ plugged-flask ” experiment, may be 
instructively varied in the following manner, which is a simplification of Pasteur’s 
bent-tube experiment. A glass-tube ( a b, fig. 1), 4 inches long, is bent at one end 
into a U-shape. The longer limb of the tube is then tightly wrapped round with 
cotton-wool so as to form a plug. This plug is inserted into the neck of a flask * half 
* The flasks used in this and the “ plugged-flask ” experiments were the ordinary four-ounce flasks used by 
chemists. 
