[Illustration with caption:  Fig. 12]

One of the best methods that can be employed for the

microscopical examination of these vibrios, quite out of contact with air, is the following.  After butyric fermentation has been going on for several days in a flask, (Fig. 13), we connect this flask by an india-rubber tube with one of the flattened bulbs previously described, which we then place on the stage of the microscope (Fig. 13).  When we wish to make an observation we close, under the mercury, at the point B, the end of the drawn-out and bent delivery-tube.  The continued evolution of gas soon exerts such a pressure within the flask, that when we open the tap R, the liquid is driven into the bulb LL, until it becomes quite full and the liquid flows over into the glass V. In this manner we may bring the vibrios under observation without their coming into contact with the least trace of air, and with as much success as if the bulb, which takes the place of an object glass, had been plunged into the very centre of the flask.  The movements and fissiparous multiplication of the vibrios may thus be seen in all their beauty, and it is indeed a most interesting sight.  The movements do not immediately cease when the temperature is suddenly lowered, even to a considerable extent, 15 degrees C. (59 degrees F.) for example; they are only slackened.  Nevertheless, it is better to observe them at the temperatures most favourable to fermentation, even in the oven where the vessels employed in the experiment are kept at a temperature between 25 degrees C. and 30 degrees C. (77 degrees F. and 86 degrees F.).

[Illustration:  Fig. 13]

We may now continue our account of the fermentation which we were studying when we made this last digression.  On June 17th that fermentation produced three times as much gas as it did on June 11th, when the residue of hydrogen, after absorption by potash, was 72.6 per cent.; whilst on the 17th it was only 49.2 per cent.  Let us again discuss the microscopic aspect of the turbid liquid at this stage.  Appended is the sketch we made (Fig. 14) and our notes on it:  “A most beautiful object:  vibrios all in motion, advancing or undulating.  They have grown considerably in bulk and length since the 11th; many of them are joined together in long sinuous chains, very mobile at the articulations, visibly less active and more wavering in proportion to the number that go to form the chain, of the length of the individuals.”  This description is applicable to the majority of the vibrios which occur in cylindrical rods and are homogeneous in aspect.  There are others, of rare occurrence in chains, which have a clear corpuscle, that is to say, a portion more refractive than other parts of the segments, at one of their extremities.  Sometimes the foremost segment has the corpuscle at one end, sometimes the other.  The long segments of the commoner kind attain a length of from 10 to 30 and even 45 thousandths of a millimetre.  Their diameter is from 1 1/2 to 2, very rarely 3, thousandths of a millimetre. [Footnote:  1 millimetre = 0.039 inch:  hence the dimensions indicated will be—­length, from 0.00039 to 0.00117, or even 0.00176 in.; diameter, from 0.000058 to 0.000078, rarely 0.000117 in.—­D.  C. R.]