that in which they had been bred--it soon becomes quite impossible to distinguish those which have been added from those which arise in the fluid. Taking into consideration the fate of other simple organisms, however, it is by no means improbable that they should be killed even by a short desiccation. I have found, for instance, that desiccation for half-an-hour in a room at a temperature of 65° F. suffices to kill all the larger, naked, lower organisms with which I have experimented--including long Vibrios, Amœbæ, Monads, Chlamydomonads, Euglenæ, Desmids, Vorticellæ and all other Ciliated Infusoria. [21] ‘Philosophical Transactions,’ 1866, pp. 616–619. But, certain indirect evidence seems to speak most authoritatively against the supposition that the air contains any notable quantity of living _Bacteria_, or _Bacteria_ germs, whether visible or invisible. I have always found that a simple solution of ammonic tartrate, which has been placed--without previous boiling--in a corked bottle of greater capacity, will become turbid in two or three days, owing to the presence of myriads of _Bacteria_; whilst a similar solution, previously boiled, may remain for ten days, three weeks, or more, without showing the least trace of turbidity, although the open neck of the bottle or flask in which it is contained, may be covered only by a loose cap of paper. And yet, at any time, in order to make this fluid become turbid in from 24 to 48 hours, all that one has to do is to bring it into contact with a small glass rod which has just been dipped into a solution containing living _Bacteria_.[22] [22] The solution, during the whole time, being exposed to a temperature of 75° to 85° F. If we find that an eminently inoculable fluid will remain for two or three weeks, or perhaps more, in contact with the air without becoming turbid, though it will always become turbid in two or three days if brought into contact with living _Bacteria_, what can we conclude, but that living _Bacteria_ are not very common in the atmosphere? These most striking facts can be easily verified by other observers.