262 
M. A. CHATJVEAU. 
dition. Then, in the vacuum, the cultures prepared for attenua¬ 
tion modify themselves in a remarkable, regulated manner, under 
the influence of heat. From zero to -j- 50°, this influence reaches 
its extreme result, that is, the death of the microbes, in a length 
of time varying from 15 to 20 days down to a few hours. From 
the experiments of M. Bert, the increase of pressure of oxygen 
must also be placed amongst the agenesical conditions. 
9th. If the temperature goes beyond the well known limits of 
the engenesy, it becomes first dysgenesical, then agenesical, and 
then has a powerful attenuating influence upon the cultures, either 
exclusively by itself, or with the assistance of the oxygen. The 
influence of this last is not very great, so far as attenuating force, 
only in the cases where the agenesy is due to the" lowering of the 
temperature ; and again this influence is of little activity. When 
the agenesy depends upon the elevation of the temperature, the 
pressure of oxygen, instead of assisting, diminishes attenuation 
very sensibly. 
10th. It is, then, especially by excess of heat, in the absence 
of oxygen, that cultures become attenuated, altered or die; on 
the other hand, if the oxygen acts but little, by its pressure, as 
debilitating, it is when heat is missing. Thence it is seen that to 
produce their maximum of action, in adding their effects together, 
the two attenuating agents, heat and oxygen, must be placed in 
respectively inverse conditions. 
11th. Material alterations always take place in the substance 
of the bacilli , whose activity is destroyed or only diminished by 
the fact of an attenuating cause—segmentation and partial dispa- 
rition of the protoplasm, or its transformation in pseudo spores. 
At times these alterations are light and cannot give an idea of 
the serious effect produced on the physiological properties. 
12th. Any culture prepared in typical conditions, that is to 
say, arrested in its development, after twenty hours of exposure 
to heat, -f- 42° 43°, and which has gone through an agenesical 
period, during which a certain attenuation has taken place, re¬ 
vives and completes its growth when it is placed again in engen- 
esical conditions. In the same way a second culture, containing 
the attenuated bacilli of the first culture, develops itself perfectly 
