1876.] Phenomena of Putrefaction and Infection. 179 



each of which was dropped a short test-tube. On October 23 thirty of 

 these tubes were filled with an infusion of hay, thirty-five with an 

 infusion of turnip, and thirty-five with an infusion of beef. The tubes 

 with their infusions had been previously boiled, ten at a time, in an oil- 

 bath. One hundred circles were marked on paper, so as to form a map 

 of the tray, and every day the state of each tube was registered upon the 

 corresponding circle. In the following description the term " cloudy " 

 is used to denote the first stage of turbidity, distinct but not strong ; 

 the term " muddy " is used to denote thick turbidity. 



One tube of the 100 was first singled out and rendered muddy. It 

 belonged to the beef group, and it was a whole day in advance of all the 

 other tubes. The progress of putrefaction was first registered on the 

 26th of October. The " map " then taken may be thus described : — 



Hay. — Of the thirty specimens exposed one had become "muddy" — 

 the seventh in the middle row reckoning from the side of the tray nearest 

 a stove. Six tubes remained perfectly clear between this muddy one 

 and the stove, proving that differences of warmth may be overridden by 

 other causes. Every one of the other tubes containing the hay-infusion 

 showed spots of mould upon the clear liquid. 



Turnip. — Four of the thirty-five tubes were very muddy, two of them 

 being in the row next the stove, one four rows distant, and the remain- 

 ing one seven rows away. Besides these, six tubes had become clouded. 

 There was no mould on any of the tubes. 



Beef. — One tube of the thirty-five was quite muddy, in the seventh 

 row from the stove. There were three cloudy tubes, while seven of them 

 bore spots of mould. 



As a general rule organic infusions exposed to the air during the 

 autumn remained for two days or more perfectly clear. Doubtless from 

 the first germs fell into them, but they required time to be hatched. This 

 period of clearness may be called the " period of latency," and indeed it 

 exactly corresponds with what is understood by this term in medicine. 

 Towards the end of the period of latency the fall into a state of disease 

 is comparatively sudden, the infusion passing from perfect clearness to 

 cloudiness more or less dense in a few hours. 



Thus the tube placed in Mr. Darwin's possession was clear at 8.30 

 a.m. on the 19th of October, and cloudy at 4.30 p.m. Seven hours, 

 moreover, after the first record of our tray of tubes, a marked change 

 had occurred. It may be thus described : — Instead of one, eight of the 

 tubes containing hay-infusion had fallen into uniform muddiness. 

 Twenty others had produced Bacterial slime, which had fallen to the 

 bottom, every tube containing the slime being covered by mould. Three 

 tubes only remained clear, but with mould upon their surfaces. The 

 muddy turnip-tubes had increased from four to ten ; seven tubes were 

 clouded, while eighteen of them remained clear, with here and there a 

 speck of mould on the surface. Of the beef, six were cloudy and one 



