i 4 4 THE POPULAR SCIENCE MONTHLY. 



the vibrios which provoke the butyric-acid fermentation. This is 

 most simply illustrated by the following beautiful observation of Pas- 

 teur : You know the way of looking at these small organisms through 

 the microscope. A drop of the liquid containing them is placed 

 upon glass, and on the drop is placed a circle of exceedingly thin 

 glass ; for, to magnify them sufficiently, it is necessary that the mi- 

 croscope should come very close to the organisms. Round the edge 

 of the circular plate of glass the liquid is in contact with the air, 

 and incessantly absorbs it, including the oxygen. Here, if the drop 

 be charged with bacteria, we have a zone of very lively ones. But 

 through this living zone, greedy of oxygen and appropriating it, the 

 vivifying gas cannot penetrate to the centre of the film. In the mid- 

 dle, therefore, the bacteria die, while their peripheral colleagues con- 

 tinue active. If a bubble of air chance to be inclosed in the film, 

 round it the bacteria will pirouette and wabble until its oxygen has 

 been absorbed, after which all their motions cease. Precisely the 

 reverse of all this occurs with the vibrios of butyric acid. In their 

 case it is the peripheral organisms that are first killed, the central 

 ones remaining vigorous while ringed by a zone of dead. Pasteur, 

 moreover, filled two vessels with a liquid containing these vibrios : 

 through one vessel he led air, and killed its vibrios in half an hour ; 

 through the other he led carbonic acid, and after three hours found 

 the vibrios fully active. It was while observing these differences of 

 deportment fifteen years ago that the thought of life without air, and 

 its bearing upon the theory of fermentation, flashed upon the mind of 

 this admirable investigator. 



And here I am tempted to inquire how it is that during the last 

 five or six years so many of the cultivated English and American pub- 

 lic, including members of the medical profession and contributors to 

 some of our most intellectual journals, could be so turned aside as 

 they have been from the pure well-spring of scientific truth to be 

 found in the writings of Pasteur ? The reason I take to be, that, 

 while against unsound logic a healthy mind can always defend itself, 

 against unsound experiment without discipline it is defenseless. To 

 judge of the soundness of scientific data, and to reason from data 

 assumed to be sound, are two totally different things. The one 

 deals with the raw material of fact, the other with the logical text- 

 ures woven from that material. Now, the logical loom may go accu- 

 rately through all its motions, while the woven fibres may be all rot- 

 ten. It is this inability, through lack of education in experiment, to 

 judge of the soundness of experimental work, which lies at the root 

 of the defection from Pasteur. 



I will cite an example of this mistake of judgment. Between the 

 large-type articles and the reviews of the Saturday Review essays on 

 various subjects are interpolated. On Alpine slopes and in the calm 

 of summer evenings, while reading these brief essays, I have been 



