84 REVIEW. 



possesses a gelatinous envelope, which is not easily affected by 

 water. But development goes no further in the same infusion ; 

 if some be, however, put with an infusion which has not passed 



Tig. 1. Spore-formation in the Bacillus of tlie hay infusion, x 1650. 

 Cohn's drawing. 



through the baciUar fermentation, the spores will be seen to 

 swell, and to push out at one end a tail, so that they become 

 "kopfchenbacterien,'^ like in appearance to the spermatozoa of ver- 

 tebrates ;i the highly refractive bodies disappear, the tail begins 

 to move and to get itself jointed; soon— but care must be taken 

 to keep out Bacter'mm termo — felted masses of bacillar fibres 

 will be evident to the naked eye. 



It will be interesting to follow Cohn into the note which he 

 appends to this paragraph, for the purpose of drawing attention 

 to the striking analogies between this bacillar fermentation of 

 hay infusions and the course of many infectious diseases ; incu- 

 bation in the former lasts for twenty-four hours, during which 

 time the affected fluid is apparently unchanged, although the 

 most active increase in number of Bacilli is in progress; on the 

 third day the paroxysm — represented by the troubled appearance 

 of the fluid — is reached ; the remission — represented by the 

 clearing of the fluid — sets in on the fourth day, when spore 

 formation commences. A few days later all is over; the ferment 

 organisms have passed into the spore state; henceforward the 

 fluid is safe from this form of fermentation, but may be highly 

 infectious to others. 



6. The conclusions to which Cohn is led are : 



(1) In boiled fluids B. termo is not developed, nor is any 

 other organism, as far as we yet know, save only Bacillus ; and 

 this is not because the fluids after boiling are incapable of sup- 

 plying nutrition to these Bacteria, as the mere dropping of some 

 8chizophjtm into a boiled infusion will show ; but for the simple 

 reason, that a temperature much higher than 50° causes their pro- 

 toplasm to coagulate. 



(2) If Bacilli become developed in the boiled hay iiifusions, it 

 is because their 7)wde of development protects them from the in- 



Jlnevceof heat. The spores, the history of which M'e have already 



I Fig. 6, PI. XX, ' Quart. Journ. Micr. Sci.,' July, 1S70. 



